1
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Stachelska-Wierzchowska A, Wierzchowski J. Chemo-Enzymatic Generation of Highly Fluorescent Nucleoside Analogs Using Purine-Nucleoside Phosphorylase. Biomolecules 2024; 14:701. [PMID: 38927104 PMCID: PMC11201700 DOI: 10.3390/biom14060701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2024] [Revised: 06/08/2024] [Accepted: 06/10/2024] [Indexed: 06/28/2024] Open
Abstract
Chemo-enzymatic syntheses of strongly fluorescent nucleoside analogs, potentially applicable in analytical biochemistry and cell biology are reviewed. The syntheses and properties of fluorescent ribofuranosides of several purine, 8-azapurine, and etheno-purine derivatives, obtained using various types of purine nucleoside phosphorylase (PNP) as catalysts, as well as α-ribose-1-phosphate (r1P) as a second substrate, are described. In several instances, the ribosylation sites are different to the canonical purine N9. Some of the obtained ribosides show fluorescence yields close to 100%. Possible applications of the new analogs include assays of PNP, nucleoside hydrolases, and other enzyme activities both in vitro and within living cells using fluorescence microscopy.
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Affiliation(s)
| | - Jacek Wierzchowski
- Department of Physics and Biophysics, University of Warmia and Mazury in Olsztyn, 10-719 Olsztyn, Poland;
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2
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Kanai R, Vilsen B, Cornelius F, Toyoshima C. Crystal structures of Na + ,K + -ATPase reveal the mechanism that converts the K + -bound form to Na + -bound form and opens and closes the cytoplasmic gate. FEBS Lett 2023; 597:1957-1976. [PMID: 37357620 DOI: 10.1002/1873-3468.14689] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2023] [Revised: 06/08/2023] [Accepted: 06/08/2023] [Indexed: 06/27/2023]
Abstract
Na+ ,K+ -ATPase (NKA) plays a pivotal role in establishing electrochemical gradients for Na+ and K+ across the cell membrane by alternating between the E1 (showing high affinity for Na+ and low affinity for K+ ) and E2 (low affinity to Na+ and high affinity to K+ ) forms. Presented here are two crystal structures of NKA in E1·Mg2+ and E1·3Na+ states at 2.9 and 2.8 Å resolution, respectively. These two E1 structures fill a gap in our description of the NKA reaction cycle based on the atomic structures. We describe how NKA converts the K+ -bound E2·2K+ form to an E1 (E1·Mg2+ ) form, which allows high-affinity Na+ binding, eventually closing the cytoplasmic gate (in E1 ~ P·ADP·3Na+ ) after binding three Na+ , while keeping the extracellular ion pathway sealed. We now understand previously unknown functional roles for several parts of NKA and that NKA uses even the lipid bilayer for gating the ion pathway.
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Affiliation(s)
- Ryuta Kanai
- Institute for Quantitative Biosciences, The University of Tokyo, Bunkyo-ku, Japan
| | - Bente Vilsen
- Department of Biomedicine, Aarhus University, Denmark
| | | | - Chikashi Toyoshima
- Institute for Quantitative Biosciences, The University of Tokyo, Bunkyo-ku, Japan
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3
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Fruergaard MU, Dach I, Andersen JL, Ozol M, Shasavar A, Quistgaard EM, Poulsen H, Fedosova NU, Nissen P. The Na,K-ATPase in complex with beryllium fluoride mimics an ATPase phosphorylated state. J Biol Chem 2022; 298:102317. [PMID: 35926706 PMCID: PMC9485054 DOI: 10.1016/j.jbc.2022.102317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2022] [Revised: 07/23/2022] [Accepted: 07/25/2022] [Indexed: 10/29/2022] Open
Abstract
The Na+,K+-ATPase generates electrochemical gradients of Na+ and K+ across the plasma membrane via a functional cycle that includes various phosphoenzyme intermediates. However, the structure and function of these intermediates and how metal fluorides mimick them require further investigation. Here, we describe a 4.0 Å resolution crystal structure and functional properties of the pig kidney Na+,K+-ATPase stabilized by the inhibitor beryllium fluoride (denoted E2-BeFx). E2-BeFx is expected to mimic properties of the E2P phosphoenzyme, yet with unknown characteristics of ion and ligand binding. The structure resembles the E2P form obtained by phosphorylation from inorganic phosphate (Pi) and stabilized by cardiotonic steroids, including a low-affinity Mg2+ site near ion binding site II. Our anomalous Fourier analysis of the crystals soaked in Rb+ (a K+ congener) followed by a low-resolution rigid-body refinement (6.9-7.5 Å) revealed pre-occlusion transitions leading to activation of the dephosphorylation reaction. We show that the Mg2+ location indicates a site of initial K+ recognition and acceptance upon binding to the outward-open E2P state after Na+ release. Furthermore, using binding and activity studies, we find that the BeFx-inhibited enzyme is also able to bind ADP/ATP and Na+. These results relate the E2-BeFx complex to a transient K+- and ADP-sensitive E*P intermediate of the functional cycle of the Na+,K+-ATPase, prior to E2P.
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Affiliation(s)
- Marlene U Fruergaard
- DANDRITE - Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Dept. Molecular Biology and Genetics, DK - 8000 Aarhus C, Denmark
| | - Ingrid Dach
- DANDRITE - Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Dept. Molecular Biology and Genetics, DK - 8000 Aarhus C, Denmark
| | - Jacob L Andersen
- DANDRITE - Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Dept. Molecular Biology and Genetics, DK - 8000 Aarhus C, Denmark; Department of Biomedicine, Aarhus University, DK - 8000 Aarhus C, Denmark
| | - Mette Ozol
- DANDRITE - Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Dept. Molecular Biology and Genetics, DK - 8000 Aarhus C, Denmark
| | - Azadeh Shasavar
- DANDRITE - Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Dept. Molecular Biology and Genetics, DK - 8000 Aarhus C, Denmark
| | - Esben M Quistgaard
- DANDRITE - Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Dept. Molecular Biology and Genetics, DK - 8000 Aarhus C, Denmark
| | - Hanne Poulsen
- DANDRITE - Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Dept. Molecular Biology and Genetics, DK - 8000 Aarhus C, Denmark
| | - Natalya U Fedosova
- Department of Biomedicine, Aarhus University, DK - 8000 Aarhus C, Denmark.
| | - Poul Nissen
- DANDRITE - Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Dept. Molecular Biology and Genetics, DK - 8000 Aarhus C, Denmark.
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4
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Faraj SE, Valsecchi WM, Cerf NT, Fedosova NU, Rossi RC, Montes MR. The interaction of Na +, K +, and phosphate with the gastric H,K-ATPase. Kinetics of E1-E2 conformational changes assessed by eosin fluorescence measurements. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1863:183477. [PMID: 32949561 DOI: 10.1016/j.bbamem.2020.183477] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 04/17/2020] [Revised: 09/10/2020] [Accepted: 09/11/2020] [Indexed: 12/12/2022]
Abstract
H,K-ATPase and Na,K-ATPase show the highest degree of sequence similarity among all other members of the P-type ATPases family. To explore their common features in terms of ligand binding, we evaluated conformational transitions due to the binding of Na+, K+ and Pi in the H,K-ATPase, and compared the results with those obtained for the Na,K-ATPase. This work shows that eosin fluorescence time courses provide a reasonably precise method to study the kinetics of the E1-E2 conformational changes in the H,K-ATPase. We found that, although Na+ shifts the equilibrium toward the E1 conformation and seems to compete with H+ in ATPase activity assays, it was neither possible to isolate a Na+-occluded state, nor to reveal an influx of Na+ related to H,K-ATPase activity. The high rate of the E2K → E1 transition found for the H,K-ATPase, which is not compatible with the presence of a K+-occluded form, agrees with the negligible level of occluded Rb+ (used as a K+ congener) found in the absence of added ligands. The use of vanadate and fluorinated metals to induce E2P-like states increased the level of occluded Rb+ and suggests that-during dephosphorylation-the probability of K+ to remain occluded increases from the E2P-ground to the E2P-product state. From kinetic experiments we found an unexpected increase in the values of kobs for E2P formation with [Pi]; consequently, to obey the Albers-Post model, the binding of Pi to the E2 state cannot be a rapid-equilibrium reaction.
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Affiliation(s)
- S E Faraj
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Buenos Aires, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - Universidad de Buenos Aires, Instituto de Química y Fisicoquímica Biológicas "Prof. Alejandro C. Paladini" (IQUIFIB), Buenos Aires, Argentina
| | - W M Valsecchi
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Buenos Aires, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - Universidad de Buenos Aires, Instituto de Química y Fisicoquímica Biológicas "Prof. Alejandro C. Paladini" (IQUIFIB), Buenos Aires, Argentina
| | - N T Cerf
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Buenos Aires, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - Universidad de Buenos Aires, Instituto de Química y Fisicoquímica Biológicas "Prof. Alejandro C. Paladini" (IQUIFIB), Buenos Aires, Argentina
| | - N U Fedosova
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - R C Rossi
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Buenos Aires, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - Universidad de Buenos Aires, Instituto de Química y Fisicoquímica Biológicas "Prof. Alejandro C. Paladini" (IQUIFIB), Buenos Aires, Argentina
| | - M R Montes
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Buenos Aires, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - Universidad de Buenos Aires, Instituto de Química y Fisicoquímica Biológicas "Prof. Alejandro C. Paladini" (IQUIFIB), Buenos Aires, Argentina.
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5
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Mishra NK, Habeck M, Kirchner C, Haviv H, Peleg Y, Eisenstein M, Apell HJ, Karlish SJD. Molecular Mechanisms and Kinetic Effects of FXYD1 and Phosphomimetic Mutants on Purified Human Na,K-ATPase. J Biol Chem 2015; 290:28746-59. [PMID: 26429909 DOI: 10.1074/jbc.m115.687913] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Indexed: 11/06/2022] Open
Abstract
Phospholemman (FXYD1) is a single-transmembrane protein regulator of Na,K-ATPase, expressed strongly in heart, skeletal muscle, and brain and phosphorylated by protein kinases A and C at Ser-68 and Ser-63, respectively. Binding of FXYD1 reduces Na,K-ATPase activity, and phosphorylation at Ser-68 or Ser-63 relieves the inhibition. Despite the accumulated information on physiological effects, whole cell studies provide only limited information on molecular mechanisms. As a complementary approach, we utilized purified human Na,K-ATPase (α1β1 and α2β1) reconstituted with FXYD1 or mutants S63E, S68E, and S63E,S68E that mimic phosphorylation at Ser-63 and Ser-68. Compared with control α1β1, FXYD1 reduces Vmax and turnover rate and raises K0.5Na. The phosphomimetic mutants reverse these effects and reduce K0.5Na below control K0.5Na. Effects on α2β1 are similar but smaller. Experiments in proteoliposomes reconstituted with α1β1 show analogous effects of FXYD1 on K0.5Na, which are abolished by phosphomimetic mutants and also by increasing mole fractions of DOPS in the proteoliposomes. Stopped-flow experiments using the dye RH421 show that FXYD1 slows the conformational transition E2(2K)ATP → E1(3Na)ATP but does not affect 3NaE1P → E2P3Na. This regulatory effect is explained simply by molecular modeling, which indicates that a cytoplasmic helix (residues 60-70) docks between the αN and αP domains in the E2 conformation, but docking is weaker in E1 (also for phosphomimetic mutants). Taken together with previous work showing that FXYD1 also raises binding affinity for the Na(+)-selective site III, these results provide a rather comprehensive picture of the regulatory mechanism of FXYD1 that complements the physiological studies.
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Affiliation(s)
| | | | - Corinna Kirchner
- the Department of Biology, University of Konstanz, 78464 Konstanz, Germany
| | - Haim Haviv
- From the Department of Biological Chemistry
| | - Yoav Peleg
- Israel Structural Proteomics Center, Weizmann Institute of Science, Rehovot 7610001, Israel and
| | | | - Hans Juergen Apell
- the Department of Biology, University of Konstanz, 78464 Konstanz, Germany
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6
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Abstract
When the Na,K-ATPase pumps at each turnover two K(+) ions into the cytoplasm, this translocation consists of several reaction steps. First, the ions diffuse consecutively from the extracellular phase through an access pathway to the binding sites where they are coordinated. In the next step, the enzyme is dephosphorylated and the ions are occluded inside the membrane domain. The subsequent transition to the E1 conformation produces a deocclusion of the binding sites to the cytoplasmic side of the membrane and allows in the last steps ion dissociation and diffusion to the aqueous phase. The interaction and competition of K(+) with various quaternary organic ammonium ions have been used to gain insight into the molecular mechanism of the ion binding process from the extracellular side in the P-E2 conformation of the enzyme. Using the electrochromic styryl dye RH421, evidence has been obtained that the access pathway consists of a wide and water-filled funnel-like part that is accessible also for bulky cations such as the benzyltriethylammonium ion, and a narrow part that permits passage only of small cations such as K(+) and NH4(+) in a distinct electrogenic way. Benzyltriethylammonium ions inhibit K(+) binding in a competitive manner that can be explained by a stopper-like function at the interface between the wide and narrow parts of the access pathway. In contrast to other quaternary organic ammonium ions, benzyltriethylammonium ions show a specific binding to the ion pump in a position inside the access pathway where it blocks effectively the access to the binding sites.
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Affiliation(s)
| | - Hans-Jürgen Apell
- Department of Biology, University of Konstanz, 78464 Konstanz, Germany
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7
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Abstract
Chemical kinetics underwent a revolution in the 1950–60s with the development by Manfred Eigen of relaxation kinetic techniques and theory for the analysis of the results obtained. The techniques he introduced extended the time scale of measurable reactions into the microsecond range and beyond. Since then, computing power has increased astronomically. Some of the approximations traditionally used in the analysis of relaxation kinetic data to reduce mathematical complexity are, therefore, now no longer a necessity. Numerical integration of coupled series of differential rate equations can be performed in seconds or less on desk-top computers. In research on the mechanism of the Na+,K+-ATPase, it has been found that traditional approaches to relaxation kinetic data can sometimes lead to erroneous conclusions or to an incomplete description of the mechanism. Therefore, one needs to be flexible in one’s approach to kinetic data analysis and carefully consider the validity of any approximations used.
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8
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Belogus T, Haviv H, Karlish SJD. Neutralization of the charge on Asp 369 of Na+,K+-ATPase triggers E1 <--> E2 conformational changes. J Biol Chem 2009; 284:31038-51. [PMID: 19726667 DOI: 10.1074/jbc.m109.050054] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
This work investigates the role of charge of the phosphorylated aspartate, Asp(369), of Na(+),K(+)-ATPase on E(1) <--> E(2) conformational changes. Wild type (porcine alpha(1)/His(10)-beta(1)), D369N/D369A/D369E, and T212A mutants were expressed in Pichia pastoris, labeled with fluorescein 5'-isothiocyanate (FITC), and purified. Conformational changes of wild type and mutant proteins were analyzed using fluorescein fluorescence (Karlish, S. J. (1980) J. Bioenerg. Biomembr. 12, 111-136). One central finding is that the D369N/D369A mutants are strongly stabilized in E(2) compared with wild type and D369E or T212A mutants. Stabilization of E(2)(Rb) is detected by a reduced K(0.5)Rb for the Rb(+)-induced E(1) <--> E(2)(2Rb) transition. The mechanism involves a greatly reduced rate of E(2)(2Rb) --> E(1)Na with no effect on E(1) --> E(2)(2Rb). Lowering the pH from 7.5 to 5.5 strongly stabilizes wild type in E(2) but affects the D369N mutant only weakly. Thus, this "Bohr" effect of pH on E(1) <--> E(2) is due largely to protonation of Asp(369). Two novel effects of phosphate and vanadate were observed with the D369N/D369A mutants as follows. (a) E(1) --> E(2).P is induced by phosphate without Mg(2+) ions by contrast with wild type, which requires Mg(2+). (b) Both phosphate and vanadate induce rapid E(1) --> E(2) transitions compared with slow rates for the wild type. With reference to crystal structures of Ca(2+)-ATPase and Na(+),K(+)-ATPase, negatively charged Asp(369) favors disengagement of the A domain from N and P domains (E(1)), whereas the neutral D369N/D369A mutants favor association of the A domain (TGES sequence) with P and N domains (E(2)). Changes in charge interactions of Asp(369) may play an important role in triggering E(1)P(3Na) <--> E(2)P and E(2)(2K) --> E(1)Na transitions in native Na(+),K(+)-ATPase.
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Affiliation(s)
- Talya Belogus
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
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9
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Mechanism of allosteric effects of ATP on the kinetics of P-type ATPases. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2009; 39:3-17. [PMID: 19225774 DOI: 10.1007/s00249-009-0407-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2008] [Revised: 12/14/2008] [Accepted: 12/14/2008] [Indexed: 10/21/2022]
Abstract
The roles of allosteric effects of ATP and protein oligomerisation in the mechanisms of P-type ATPases belong to the most controversial and least well understood topics in the field. Recent crystal structural and kinetic data, however, now allow certain hypotheses to be definitely excluded and consistent hypotheses to be developed. The aim of this review is to critically discuss recent results and, in the light of them, to present a set of conclusions which could form the basis of future research. The major conclusions are: (1) at saturating ATP concentrations P-type ATPases function as monomeric enzymes, (2) the catalytic units of P-type ATPases only possess a single ATP binding site, (3) at non-saturating ATP concentrations P-type ATPases exist as diprotomeric (or higher oligomeric) complexes, (4) protein-protein interactions within a diprotomeric complex enhances the enzymes' ATP binding affinity, (5) ATP binding to both protomers within a diprotomeric complex causes it to dissociate into two separate monomers. The physiological role of protein-protein interactions within a diprotomer may be to enhance ATP binding affinity so as to scavenge ATP and maximize the ion pumping rate under hypoxic or anoxic conditions. For the first time a structural basis for the well-known ATP allosteric acceleration of the E2 --> E1 transition is presented. This is considered to be due to a minimization of steric hindrance between neighbouring protomers because of the ability of ATP to induce a compact conformation of the enzymes' cytoplasmic domains.
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10
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Abstract
The identification of the sodium potassium pump as a Na+, K+-ATPase is described.
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Affiliation(s)
- Jens Chr Skou
- Department of Biophysics, University of Aarhus, Ole Worms Allé 185, 8000 Aarhus C, DK, Denmark
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11
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Patzelt-Wenczler R, Schoner W. Evidence for two different reactive sulfhydryl groups in the ATP-binding sites of (Na+ + K+)-ATPase. EUROPEAN JOURNAL OF BIOCHEMISTRY 2005; 114:79-87. [PMID: 6260491 DOI: 10.1111/j.1432-1033.1981.tb06175.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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12
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Apell HJ. Structure-function relationship in P-type ATPases--a biophysical approach. Rev Physiol Biochem Pharmacol 2004; 150:1-35. [PMID: 12811587 DOI: 10.1007/s10254-003-0018-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
P-type ATPases are a large family of membrane proteins that perform active ion transport across biological membranes. In these proteins the energy-providing ATP hydrolysis is coupled to ion-transport that builds up or maintains the electrochemical potential gradients of one or two ion species across the membrane. P-type ATPases are found in virtually all eukaryotic cells and also in bacteria, and they are transporters of a broad variety of ions. So far, a crystal structure with atomic resolution is available only for one species, the SR Ca-ATPase. However, biochemical and biophysical studies provide an abundance of details on the function of this class of ion pumps. The aim of this review is to summarize the results of preferentially biophysical investigations of the three best-studied ion pumps, the Na,K-ATPase, the gastric H,K-ATPase, and the SR Ca-ATPase, and to compare functional properties to recent structural insights with the aim of contributing to the understanding of their structure-function relationship.
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Affiliation(s)
- H-J Apell
- Department of Biology, University of Konstanz, Fach M635, 78457 Konstanz, Germany.
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13
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Abstract
This article gives a history of the evidence (a) that animal cell membranes contain pumps that expel sodium ions in exchange for potassium ions; (b) that the pump derives energy from the hydrolysis of ATP; (c) that it is thermodynamically reversible-artificially steep transmembrane ion gradients make it run backward synthesizing ATP from ADP and orthophosphate; (d) that its mechanism is a ping-pong one, in which phosphorylation of the pump by ATP is associated with an efflux of three sodium ions, and hydrolysis of the phosphoenzyme is associated with an influx of two potassium ions; (e) that each half of the working cycle involves both the transfer of a phosphate group and a conformational change-the phosphate transfer being associated with the occlusion of ions bound at one surface and the conformational change releasing the occluded ions at the opposite surface.
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Affiliation(s)
- Ian M Glynn
- Trinity College, Cambridge CB2 1TQ, England.
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14
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Shin JM, Goldshleger R, Munson KB, Sachs G, Karlish SJ. Selective Fe2+-catalyzed oxidative cleavage of gastric H+,K+-ATPase: implications for the energy transduction mechanism of P-type cation pumps. J Biol Chem 2001; 276:48440-50. [PMID: 11585827 DOI: 10.1074/jbc.m106864200] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In the presence of ascorbate/H(2)O(2), Fe(2+) ions or the ATP-Fe(2+) complex catalyze selective cleavage of the alpha subunit of gastric H(+),K(+)-ATPase. The electrophoretic mobilities of the fragments and dependence of the cleavage patterns on E(1) and E(2) conformational states are essentially identical to those described previously for renal Na(+),K(+)-ATPase. The cleavage pattern of H(+),K(+)-ATPase by Fe(2+) ions is consistent with the existence of two Fe(2+) sites: site 1 within highly conserved sequences in the P and A domains, and site 2 at the cytoplasmic entrance to trans-membrane segments M3 and M1. The change in the pattern of cleavage catalyzed by Fe(2+) or the ATP-Fe(2+) complex induced by different ligands provides evidence for large conformational movements of the N, P, and A cytoplasmic domains of the enzyme. The results are consistent with the Ca(2+)-ATPase crystal structure (Protein Data Bank identification code; Toyoshima, C., Nakasako, M., Nomura, H., and Ogawa, H. (2000) Nature 405, 647-655), an E(1)Ca(2+) conformation, and a theoretical model of Ca(2+)-ATPase in an E(2) conformation (Protein Data Bank identification code ). Thus, it can be presumed that the movements of N, P, and A cytoplasmic domains, associated with the E(1) <--> E(2) transitions, are similar in all P-type ATPases. Fe(2+)-catalyzed cleavage patterns also reveal sequences involved in phosphate, Mg(2+), and ATP binding, which have not yet been shown in crystal structures, as well as changes which occur in E(1) <--> E(2) transitions, and subconformations induced by H(+),K(+)-ATPase-specific ligands such as SCH28080.
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Affiliation(s)
- J M Shin
- Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
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15
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16
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Berman MC. Slippage and uncoupling in P-type cation pumps; implications for energy transduction mechanisms and regulation of metabolism. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1513:95-121. [PMID: 11470083 DOI: 10.1016/s0005-2736(01)00356-x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
P-type ATPases couple scalar and vectorial events under optimized states. A number of procedures and conditions lead to uncoupling or slippage. A key branching point in the catalytic cycle is at the cation-bound form of E(1)-P, where isomerization to E(2)-P leads to coupled transport, and hydrolysis leads to uncoupled release of cations to the cis membrane surface. The phenomenon of slippage supports a channel model for active transport. Ability to occlude cations within the channel is essential for coupling. Uncoupling and slippage appear to be inherent properties of P-type cation pumps, and are significant contributors to standard metabolic rate. Heat production is favored in the uncoupled state. A number of disease conditions, include ageing, ischemia and cardiac failure, result in uncoupling of either the Ca(2+)-ATPase or Na(+)/K(+)-ATPase.
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Affiliation(s)
- M C Berman
- Division of Chemical Pathology, Health Sciences Faculty, University of Cape Town, Observatory 7925, Cape Town, South Africa.
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17
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De Weer P, Gadsby DC, Rakowski RF. Voltage dependence of the apparent affinity for external Na(+) of the backward-running sodium pump. J Gen Physiol 2001; 117:315-28. [PMID: 11279252 PMCID: PMC2217255 DOI: 10.1085/jgp.117.4.315] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The steady-state voltage and [Na(+)](o) dependence of the electrogenic sodium pump was investigated in voltage-clamped internally dialyzed giant axons of the squid, Loligo pealei, under conditions that promote the backward-running mode (K(+)-free seawater; ATP- and Na(+)-free internal solution containing ADP and orthophosphate). The ratio of pump-mediated (42)K(+) efflux to reverse pump current, I(pump) (both defined by sensitivity to dihydrodigitoxigenin, H(2)DTG), scaled by Faraday's constant, was -1.5 +/- 0.4 (n = 5; expected ratio for 2 K(+)/3 Na(+) stoichiometry is -2.0). Steady-state reverse pump current-voltage (I(pump)-V) relationships were obtained either from the shifts in holding current after repeated exposures of an axon clamped at various V(m) to H(2)DTG or from the difference between membrane I-V relationships obtained by imposing V(m) staircases in the presence or absence of H(2)DTG. With the second method, we also investigated the influence of [Na(+)](o) (up to 800 mM, for which hypertonic solutions were used) on the steady-state reverse I(pump)-V relationship. The reverse I(pump)-V relationship is sigmoid, I(pump) saturating at large negative V(m), and each doubling of [Na(+)](o) causes a fixed (29 mV) rightward parallel shift along the voltage axis of this Boltzmann partition function (apparent valence z = 0.80). These characteristics mirror those of steady-state (22)Na(+) efflux during electroneutral Na(+)/Na(+) exchange, and follow without additional postulates from the same simple high field access channel model (Gadsby, D.C., R.F. Rakowski, and P. De Weer, 1993. Science. 260:100-103). This model predicts valence z = nlambda, where n (1.33 +/- 0.05) is the Hill coefficient of Na binding, and lambda (0.61 +/- 0.03) is the fraction of the membrane electric field traversed by Na ions reaching their binding site. More elaborate alternative models can accommodate all the steady-state features of the reverse pumping and electroneutral Na(+)/Na(+) exchange modes only with additional assumptions that render them less likely.
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Affiliation(s)
- P De Weer
- Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA.
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18
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Kaufman SB, González-Lebrero RM, Schwarzbaum PJ, Nørby JG, Garrahan PJ, Rossi RC. Are the states that occlude rubidium obligatory intermediates of the Na(+)/K(+)-ATPase reaction? J Biol Chem 1999; 274:20779-90. [PMID: 10409617 DOI: 10.1074/jbc.274.30.20779] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In the Albers-Post model, occlusion of K(+) in the E(2) conformer of the enzyme (E) is an obligatory step of Na(+)/K(+)-ATPase reaction. If this were so the ratio (Na(+)/K(+)-ATPase activity)/(concentration of occluded species) should be equal to the rate constant for deocclusion. We tested this prediction in a partially purified Na(+)/K(+)-ATPase from pig kidney by means of rapid filtration to measure the occlusion using the K(+) congener Rb(+). Assuming that always two Rb(+) are occluded per enzyme, the steady-state levels of occluded forms and the kinetics of deocclusion were adequately described by the Albers-Post model over a very wide range of [ATP] and [Rb(+)]. The same happened with the kinetics of ATP hydrolysis. However, the value of the parameters that gave best fit differed from those for occlusion in such a way that the ratio (Na(+)/K(+)-ATPase activity)/(concentration of occluded species) became much larger than the rate constant for deocclusion when [Rb(+)] <10 mM. This points to the presence of an extra ATP hydrolysis that is not Na(+)-ATPase activity and that does not involve occlusion. A possible way of explaining this is to posit that the binding of a single Rb(+) increases ATP hydrolysis without occlusion.
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Affiliation(s)
- S B Kaufman
- Instituto de Química y Fisicoquímica Biológicas and Departamento de Química Biológica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, 1113 Buenos Aires, Argentina
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19
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Tsuda T, Kaya S, Yokoyama T, Hayashi Y, Taniguchi K. ATP and acetyl phosphate induces molecular events near the ATP binding site and the membrane domain of Na+,K+-ATPase. The tetrameric nature of the enzyme. J Biol Chem 1998; 273:24339-45. [PMID: 9733721 DOI: 10.1074/jbc.273.38.24339] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The addition of ATP to Mg2+-Na+-bound-probe labeled Na+,K+-ATPase preparations containing approximately 0.5 mol of pyridoxal 5'-diphospho-5'-adenosine (AP2PL) probe at Lys-480 and approximately 0.9 mol of fluorescein 5'-isothiocyanate (FITC) probe at Lys-501 showed a decrease and an increase in the AP2PL fluorescence intensity with neither significant ATP-dependent phosphorylation nor FITC fluorescence change. The rate constants for the fluorescence change increased nearly linearly with increasing ATP concentrations. The substitution of AcP for ATP decreased the FITC fluorescence rather monophasically, 8.5/s, which was followed by the half-site phosphorylation with same amount of components with different rate constant, 7.2 and 4.6/s, followed by a much slower increase in the two components of AP2PL fluorescence, 1.4 and 0.2/s. The addition of Na+ with increasing concentrations of ATP to the K+-bound AP2PL-FITC enzymes induced accelerations in the decrease and an increase in the AP2PL fluorescence intensity with two different increases in the FITC fluorescence intensity, showing that the same concentration of ATP is capable of inducing four different fluorescence changes. The addition of ATP to the Mg2+-Na+-bound enzymes modified with N-[p-(2-benzimidazolyl)phenyl]-maleimide (BIPM) at Cys-964 and retaining full Na+,K+-ATPase activity induced two different increases in BIPM fluorescence intensity. Each rate constant for the BIPM fluorescence change versus concentrations of ATP gave two intersecting straight lines. These data and the stoichiometries of fluorescence probe bindings and ATP- and AcP-dependent phosphorylation provide strong support for the conclusion that the functional membrane-bound Na+,K+-ATPase is a tetramer.
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Affiliation(s)
- T Tsuda
- Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060, Japan
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20
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21
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Gropp T, Cornelius F, Fendler K. K+-dependence of electrogenic transport by the NaK-ATPase. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1368:184-200. [PMID: 9459597 DOI: 10.1016/s0005-2736(97)00162-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Charge translocation by the NaK-ATPase from shark rectal gland was measured by adsorption of proteoliposomes to a planar lipid membrane. The proteoliposomes were prepared by reconstitution of purified NaK-ATPase into liposomes consisting of E. coli lipids. The protein was activated by applying an ATP concentration jump produced by photolysis of a protected derivative of ATP, caged ATP. K+ titrations were used to study the effect of K+ on the charge translocation kinetics of the protein. The time-dependent currents obtained after activation of the enzyme with caged ATP were analyzed with a simplified Albers-Post model (E1 (k1)-->E1ATP (k2)-->E2P (k3)-->E1) taking into account the capacitive coupling of the protein to the measuring system. The results of the K+ titrations show a strong dependence of the rate constant k3 on the K+ concentration at the extracellular side of the protein, indicating the K+ activated dephosphorylation reaction. In contrast, k1 and k2 remained constant. The K+ dependence of the rate k3 could be well described with a K+ binding model with two equivalent binding sites (E2P + 2K+ <==> E2P(K) + K+ <==> E2 P(2K)) followed by a rate limiting reaction (E2P(2K) --> E1(2K)). The half saturating K+ concentration K3,0.5 and the microscopic dissociation constant K3 for the K+ dependence of k3 were 4.5mM and 1.9mM respectively. At saturating K+ concentration the rate constant k3 was approximately 100 s(-1). The relative amount of net charge transported during the Na+ and the K+ dependent reactions could be determined from the experiments. Our results suggest electroneutral K+ translocation and do not support electrogenic K+ binding in an extracellular access channel. This is compatible with a model where 2 negative charges are cotransported with 3Na+ and 2K+ ions. Error analysis gives an upper limit of 20% charge transported during K+ translocation or during electrogenic K+ binding in a presumptive access channel compared to Na+ translocation.
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Affiliation(s)
- T Gropp
- Max-Plank-Institut für Biophysik, Frankfurt, Germany
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22
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The ATP Binding Sites of P-Type ION Transport ATPases: Properties, Structure, Conformations, and Mechanism of Energy Coupling. ACTA ACUST UNITED AC 1997. [DOI: 10.1016/s1569-2558(08)60152-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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23
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Pratap PR, Palit A, Grassi-Nemeth E, Robinson JD. Kinetics of conformational changes associated with potassium binding to and release from Na+/K(+)-ATPase. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1285:203-11. [PMID: 8972704 DOI: 10.1016/s0005-2736(96)00162-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The Na+/K(+)-ATPase functions in cells to couple energy from the hydrolysis of ATP to the transport Na+ out and K+ in. The fluorescent probe IAF (iodoacetamidofluorescein) covalently binds to this enzyme, reporting conformational changes without inhibiting enzyme activity. This paper describes experiments using dog kidney enzyme labeled with IAF to examine kinetics of conformational changes resulting from added Na+ and K+, measured in terms of steady-state and stopped-flow fluorescence changes. Kinetics of these fluorescence changes were examined as a function of temperature from two initial conditions: (a) enzyme in the high-fluorescence form (E(high)) was rapidly mixed with varying [K+]; and (b) enzyme in the low-fluorescence form (E(low)) was rapidly mixed with varying [ATP]. These experiments showed: (1) The rate constant for the fluorescence change from E(high) to E(low) was much larger than that for the opposite transition, E(low) to E(high); (2) the apparent free energy of activation (Ea(app)) for the two transitions were different (as estimated from Arrhenius plots); (3) under steady-state conditions, IAF fluorescence did not change when ATP was added to E(low)(K+) in the absence of Na+; (4) the apparent free energy of activation was independent of [K+] for the E(high) to E(low) transition (at 16.4 kcal/mol) but increased with [ATP] for the E(low) to E(high) transition; (5) Ea(app) for the E(low) to E(high) transition with 1 mM ATP was approximately the same as that in the absence of ATP (34 kcal/mol). These results can be interpreted as: (i) in the transition from E(low) to E(high), IAF reported a conformational change that occurred after K+ release to the intracellular side and which is involved in Na+ binding; (ii) Ea(app) increased with [ATP], while increasing the entropy of the transition state. Thus, ATP appeared to destabilize the enzyme during the transition from E(low) to E(high).
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Affiliation(s)
- P R Pratap
- Department of Physics and Astronomy, University of North Carolina at Greensboro 27412-5001, USA.
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24
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Arato-Oshima T, Matsui H, Wakizaka A, Homareda H. Mechanism responsible for oligomycin-induced occlusion of Na+ within Na/K-ATPase. J Biol Chem 1996; 271:25604-10. [PMID: 8810335 DOI: 10.1074/jbc.271.41.25604] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The mechanism whereby oligomycin occludes Na+ within Na/K-ATPase was investigated to study Na+ and K+ transport mechanisms. Oligomycin stimulated Na+ binding to Na/K-ATPase but inhibited Na-K and Na-Na exchange. The oligomycin concentration required to stimulate Na+ binding to half-maximal was 4.5 microM, which was close to the concentration that reduced Na-Na and Na-K exchange and ATPase activity to half-maximal, suggesting that Na/K-ATPase possesses an oligomycin binding site responsible for stimulating Na+ binding and reducing ion exchange and ATPase activity. In contrast, neither K+ binding nor K+ transport was affected by oligomycin. Limited tryptic digestion of Na/K-ATPase showed that, unlike Na+, K+, and ouabain, oligomycin treatment did not result in a specific digestion pattern. Oligomycin appeared to inhibit ouabain binding in a noncompetitive manner, whereas it did not affect ATP binding. Na/K-ATPase isoforms with low and high sensitivities to ouabain were equally sensitive to oligomycin. These results suggest that the oligomycin binding site is located on the extracellular side of Na/K-ATPase, at a different position from the ouabain binding site, and this antibiotic did not induce a conformational change of Na/K-ATPase. We propose that oligomycin interacts with the Na+ occlusion site from the extracellular side of Na/K-ATPase, which delays Na+ release to the extracellular side without inducing a conformational change, suggesting that the pathways responsible for Na+ and K+ transport differ.
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Affiliation(s)
- T Arato-Oshima
- Second Department of Biochemistry, Kyorin University School of Medicine, Mitaka, Tokyo 181, Japan
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25
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Cornelius F. Hydrophobic ion interaction on Na+ activation and dephosphorylation of reconstituted Na+,K(+)-ATPase. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1235:183-96. [PMID: 7756325 DOI: 10.1016/0005-2736(95)80004-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
In liposomes with reconstituted shark Na+,K(+)-ATPase an uncoupled Na(+)-efflux and a Na+/Na+ exchange can be induced on inside-out oriented pumps by the addition of external (cytoplasmic) Na+ and MgATP to liposomes that either do not contain Na+ (and other alkali cations), or include 130 mM Na+ internally (extracellular). Both modes of exchange are electrogenic and accompanied by a net hydrolysis of ATP. The coupling ratio of positive net charges translocated per ATP split is found to be close to 3:1 and 1:1, respectively, for the two modes of exchange reactions at pH 7.0. By addition of the hydrophobic anion tetraphenylboron (TPB-), which imposes a negative electrostatic membrane potential inside the lipid bilayer, the ATP hydrolysis accompanying uncoupled Na+ efflux is increased with increasing TPB- concentrations. Cholesterol which increases the inner positive dipole potential of the bilayer counteracted this activation by TPB- of uncoupled Na+ efflux. Using the structural analog tetraphenylphosphonium (TPP+), which elicits an inside positive membrane potential, ATP hydrolysis accompanying uncoupled Na(+)-efflux is decreased. The rate of dephosphorylation in the absence of extracellular alkali cations was affected in a similar manner, whereas the dephosphorylation in the presence of extracellular Na+ inducing Na+/Na+ exchange was unaffected by the hydrophobic ions. In both modes of exchange the phosphorylation reaction was independent of the presence of hydrophobic ions. The hydrophobic ions affected the apparent affinity for cytoplasmic Na+, indicating that binding of cytoplasmic Na+ may involve the migration of cations to binding sites through a shallow cytoplasmic access channel. The results are in accordance with the simple electrostatic model for charge translocation in which two negative charges in the cytoplasmic binding domain of the Na+,K(+)-ATPase co-migrate during cation transport.
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Affiliation(s)
- F Cornelius
- Institute of Biophysics, University of Aarhus, Denmark
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26
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Klodos I, Fedosova NU, Plesner L. Influence of intramembrane electric charge on Na,K-ATPase. J Biol Chem 1995; 270:4244-54. [PMID: 7876184 DOI: 10.1074/jbc.270.9.4244] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Effects of lipophilic ions, tetraphenylphosphonium (TPP+) and tetraphenylboron (TPB-), on interactions of Na+ and K+ with Na,K-ATPase were studied with membrane-bound enzyme from bovine brain, pig kidney, and shark rectal gland. Na+ and K+ interactions with the inward-facing binding sites, monitored by eosin fluorescence and phosphorylation, were not influenced by lipophilic ions. Phosphoenzyme interactions with extracellular cations were evaluated through K(+)-, ADP-, and Na(+)-dependent dephosphorylation. TPP+ decreased: 1) the rate of transition of ADP-insensitive to ADP-sensitive phosphoenzyme, 2) the K+ affinity and the rate coefficient for dephosphorylation of the K-sensitive phosphoenzyme, 3) the Na+ affinity and the rate coefficient for Na(+)-dependent dephosphorylation. Pre-steady state phosphorylation experiments indicate that the subsequent occlusion of extracellular cations was prevented by TPP+. TPB- had opposite effects. Effects of lipophilic ions on the transition between phosphoenzymes were significantly diminished when Na+ was replaced by N-methyl-D-glucamine or Tris+, but were unaffected by the replacement of Cl- by other anions. Lipophilic ions affected Na-ATPase, Na,K-ATPase, and p-nitrophenylphosphatase activities in accordance with their effects on the partial reactions. Effects of lipophilic ions appear to be due to their charge indicating that Na+ and K+ access to their extracellular binding sites is modified by the intramembrane electric field.
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Affiliation(s)
- I Klodos
- Institute of Biophysics, University of Aarhus, Denmark
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27
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Robinson JD, Pratap PR. Indicators of conformational changes in the Na+/K(+)-ATPase and their interpretation. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1154:83-104. [PMID: 8389590 DOI: 10.1016/0304-4157(93)90018-j] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- J D Robinson
- Department of Pharmacology State University of New York Health Science Center, Syracuse 13210
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28
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Nassi P, Marchetti E, Nediani C, Liguri G, Ramponi G. Acylphosphatase induced modifications in the functional properties of erythrocyte membrane sodium pump. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1147:19-26. [PMID: 8385494 DOI: 10.1016/0005-2736(93)90311-m] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Human red cell acylphosphatase actively hydrolyzes the Na+/K(+)-ATPase phosphoenzyme from erythrocyte membrane. This effect occurred with amounts of acylphosphatase (up to 10 units/mg membrane protein) within the physiological range, and the low value of the apparent Km (0.147 +/- 0.050 microM) indicates that the enzyme has a high affinity for this substrate. When added at the above concentration to inside out vesicles from human erythrocytes, acylphosphatase significantly enhanced the rate of strophantidine-sensitive ATP hydrolysis. The same amounts of acylphosphatase stimulated, although to a lower extent, the rate of ATP-dependent 22Na+ influx (normal efflux). Thus, the calculated stoichiometry for Na+/ATP was 2.68 in the absence of acylphosphatase and 1.06 in the presence of 10 units/mg vesicle protein of the enzyme. Conversely, acylphosphatase addition strongly decreased the rate of ATP-dependent 86Rb+(K+) efflux (normal influx) which, with 10 units/mg vesicle protein, was almost suppressed. As a consequence, the Na+/Rb+ ratio, calculated as 1.52 in the absence of acylphosphatase rose to 72.5 in the presence of 10 units/mg vesicle protein of this enzyme. These results suggest that, because of its hydrolytic activity on the phosphoenzyme intermediate, acylphosphatase 'uncouples' erythrocyte membrane Na+,K+ pump. Possible mechanisms for this effect are discussed.
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Affiliation(s)
- P Nassi
- Dipartimento di Scienze Biochimiche, Università di Firenze, Italy
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29
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Affiliation(s)
- I M Glynn
- Physiological Laboratory, University of Cambridge
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30
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Cornelius F. Cis-allosteric effects of cytoplasmic Na+/K+ discrimination at varying pH. Low-affinity multisite inhibition of cytoplasmic K+ in reconstituted Na+/K(+)-ATPase engaged in uncoupled Na(+)-efflux. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1108:190-200. [PMID: 1322175 DOI: 10.1016/0005-2736(92)90025-h] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
In liposomes with reconstituted shark Na+/K(+)-ATPase the effect of cytoplasmic K+ was investigated in the absence of extracellular alkali ions. During such conditions the Na+/K(+)-ATPase is engaged in the so called uncoupled Na+ efflux mode in which cytoplasmic Na+ activates and binds to the enzyme and becomes translocated without countertransport of K+ as in the physiological Na+/K+ exchange mode. In this uncoupled flux mode only low-affinity inhibition by K+cyt is found to be present. The inhibition pattern is consistent with a model in which cytoplasmic K+ exhibit mixed inhibition of Na+ activation, probably by binding at the three cytoplasmic loading sites on E1ATP (E1A). With determined intrinsic binding constants for cytoplasmic Na+ to this form of KS1, KS2, KS3 = 40 mM, 2 mM, 2 mM the inhibition pattern can be simulated assuming three K+cyt sites with equal affinity for Ki = 40 mM, similar to KS1 for the first Na+cyt site. The discrimination between cytoplasmic Na+ and K+ is therefore enhanced by allosteric interaction initiated from the cis-side due to binding of the first Na+, as opposed to K+, which induces the positive cooperatively in the successive Na+ bindings. pH is found to influence the pattern of K+cyt inhibition: A lowering of the pH potentiates the K+cyt inhibition, whereas at increased pH the inhibition is decreased and transformed into a pure competitive competition.
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Affiliation(s)
- F Cornelius
- Institute of Biophysics, University of Aarhus, Denmark
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31
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Abstract
The energy dependent exchange of cytoplasmic Na+ for extracellular K+ in mammalian cells is due to a membrane bound enzyme system, the Na,K-ATPase. The exchange sustains a gradient for Na+ into and for K+ out of the cell, and this is used as an energy source for creation of the membrane potential, for its de- and repolarisation, for regulation of cytoplasmic ionic composition and for transepithelial transport. The Na,K-ATPase consists of two membrane spanning polypeptides, an alpha-subunit of 112-kD and a beta-subunit, which is a glycoprotein of 35-kD. The catalytic properties are associated with the alpha-subunit, which has the binding domain for ATP and the cations. In the review, attention will be given to the biochemical characterization of the reaction mechanism underlying the coupling between hydrolysis of the substate ATP and transport of Na+ and K+.
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Affiliation(s)
- J C Skou
- Institute of Biophysics, University of Aarhus, Denmark
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32
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Repke KR, Schön R. Role of protein conformation changes and transphosphorylations in the function of Na+/K(+)-transporting adenosine triphosphatase: an attempt at an integration into the Na+/K+ pump mechanism. Biol Rev Camb Philos Soc 1992; 67:31-78. [PMID: 1318758 DOI: 10.1111/j.1469-185x.1992.tb01658.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The particular aim of the review on some basic facets of the mechanism of Na+/K(+)-transporting ATPase (Na/K-ATPase) has been to integrate the experimental findings concerning the Na(+)- and K(+)-elicited protein conformation changes and transphosphorylations into the perspective of an allosterically regulated, phosphoryl energy transferring enzyme. This has led the authors to the following summarizing evaluations. 1. The currently dominating hypothesis on a link between protein conformation changes ('E1 in equilibrium with E2') and Na+/K+ transport (the 'Albers-Post scheme') has been constructed from a variety of partial reactions and elementary steps, which, however, do not all unequivocally support the hypothesis. 2. The Na(+)- and K(+)-elicited protein conformation changes are inducible by a variety of other ligands and modulatory factors and therefore cannot be accepted as evidence for their direct participation in effecting cation translocation. 3. There is no evidence that the 'E1 in equilibrium with E2' protein conformation changes are moving Na+ and K+ across the plasma membrane. 4. The allosterically caused ER in equilibrium with ET ('E1 in equilibrium with E2') conformer transitions and the associated cation 'occlusion' in equilibrium with 'de-occlusion' processes regulate the actual catalytic power of an enzyme ensemble. 5. A host of experimental variables determines the proportion of functionally competent ER enzyme conformers and incompetent ET conformers so that any enzyme population, even at the start of a reaction, consists of an unknown mixture of these conformers. These circumstances account for the occurrence of contradictory observations and apparent failures in their comparability. 6. The modelling of the mechanism of the Na/K-ATPase and Na+/K+ pump from the results of reductionistically designed experiments requires the careful consideration of the physiological boundary conditions. 7. Na+ and K+ ligandation of Na/K-ATPase controls the geometry and chemical reactivity of the catalytic centre in the cycle of E1 in equilibrium with E2 state conversions. This is possibly effected by hinge-bending, concerted motions of three adjacent, intracellularly exposed peptide sequences, which shape open and closed forms of the catalytic centre in lock-and-key responses. 8. The Na(+)-dependent enzyme phosphorylation with ATP and the K(+)-dependent hydrolysis of the phosphoenzyme formed are integral steps in the transport mechanism of Na/K-ATPase, but the translocations of Na+ and K+ do not occur via a phosphate-cation symport mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- K R Repke
- Energy Conversion Unit, Central Institute of Molecular Biology, Berlin-Buch, Germany
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34
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Cornelius F. Functional reconstitution of the sodium pump. Kinetics of exchange reactions performed by reconstituted Na/K-ATPase. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1071:19-66. [PMID: 1848452 DOI: 10.1016/0304-4157(91)90011-k] [Citation(s) in RCA: 102] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- F Cornelius
- Institute of Biophysics, University of Aarhus, Denmark
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35
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Robinson JD, Pratap PR. Na+/K(+)-ATPase: modes of inhibition by Mg2+. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1061:267-78. [PMID: 1847828 DOI: 10.1016/0005-2736(91)90292-g] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Adding 15 mM free Mg2+ decreased Vmax of the Na+/K(+)-ATPase reaction. Mg2+ also decreased the K0.5 for K+ activation, as a mixed inhibitor, but the increased inhibition at higher K+ concentrations diminished as the Na+ concentration was raised. Inhibition was greater with Rb+ but less with Li+ when these cations substituted for K+ at pH 7.5, while at pH 8.5 inhibition was generally less and essentially the same with all three cations: implying an association between inhibition and ion occlusion. On the other hand, Mg2+ increased the K0.5 for Na(+)-activation of the Na+/K(+)-ATPase and Na(+)-ATPase reactions, as a mixed inhibitor. Changing incubation pH or temperature, or adding dimethylsulfoxide affected inhibition by Mg2+ and K0.5 for Na+ diversely. Presteady-state kinetic studies on enzyme phosphorylation, however, showed competition between Mg2+ and Na+. In the K(+)-phosphatase reaction catalyzed by this enzyme Mg2+ was a (near) competitor toward K+. Adding Na+ with K+ inhibited phosphatase activity, but under these conditions 15 mM Mg2+ stimulated rather than inhibited; still higher Mg2+ concentrations then inhibited with K+ plus Na+. Similar stimulation and inhibition occurred when Mn2+ was substituted for Mg2+, although the concentrations required were an order of magnitude less. In all these experiments no ionic substitutions were made to maintain ionic strength, since alternative cations, such as choline, produced various specific effects themselves. Kinetic analyses, in terms of product inhibition by Mg2+, require Mg2+ release at multiple steps. The data are accommodated by a scheme for the Na+/K(+)-ATPase with three alternative points for release: before MgATP binding, before K+ release and before Na+ binding. The latter alternatives necessitate two Mg2+ ions bound simultaneously to the enzyme, presumably to divalent cation-sites associated with the phosphate and the nucleotide domains of the active site.
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Affiliation(s)
- J D Robinson
- Department of Pharmacology, State University of New York, Syracuse 13210
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36
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Abstract
Relative internal concentrations of Na+ and K+ are important in regulating (Na+,K+)-ATPase in situ. Ethanol is known to inhibit (Na+,K+)-ATPase and to reduce K+ affinity, but the concentrations required for these effects in vitro are large compared with those probably attainable in vivo. Yet, there is evidence suggesting that ethanol has physiologically relevant effects on (Na+,K+)-ATPase. We have investigated the effects of ethanol on selectivity for Na+ versus K+. At 150 mM, ethanol had little effect on (Na+,K+)-ATPase activity under the usual assay conditions, slightly (but nonsignificantly) reduced K+ affinity, and had no effect on extrapolated Na+ affinity in the absence of K+. However, ethanol had marked effects on cation selectivity, doubling the Ki for K+ on Na+ affinity and halving the Ki for Na+ on K+ affinity. These data show that ethanol, at concentrations too small for effects on (Na+,K+)-ATPase activity under optimal assay conditions, can alter its responses to changes in Na+ or K+.
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Affiliation(s)
- A C Swann
- Department of Psychiatry, University of Texas Medical School, Houston 77225
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37
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Conformational transitions of the H,K-ATPase studied with sodium ions as surrogates for protons. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(17)45413-5] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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38
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Ebner F. Factors influencing the onset of ouabain inhibition of Na,K-ATPase from guinea-pig myocardium. Br J Pharmacol 1990; 101:337-43. [PMID: 2175233 PMCID: PMC1917712 DOI: 10.1111/j.1476-5381.1990.tb12711.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
1. The onset of ouabain inhibition was quantified by analysis with an integrated rate equation from experiments in which the activity of Na,K-ATPase from guinea-pig myocardium had been altered with adenosine 5'-triphosphate (ATP, 0.3-9 mmoll-1) in the absence and presence of a detergent. 2. Under control conditions with increasing ouabain (0.1-100 mumoll-1) and ATP (0.3-1 mmoll-1) concentrations, inhibition developed faster. The acceleration by ouabain became less effective at saturating concentrations leading to a non-linear relationship between pseudo-first-order rate constants of inhibition and ouabain concentration. With a rise of ATP to 3 and 9 mmoll-1, i.e., near total Mg concentration (5 mmoll-1), inhibition was retarded presumably because the free concentrations of Mg and uncomplexed ATP changed. Varying the ATP concentration had little effect on ouabain potency at steady state; Hill coefficients were less than 1. 3. The detergent alamethicin (23 micrograms ml-1) neither interfered with Na,K-ATPase activity nor with inhibition at steady state but accelerated its onset. This supports a role for a lipid barrier in the development of inhibition. 4. While the reaction of low concentrations of ouabain with the receptors seemed to govern inhibition rate, with an increase in steroid concentration in the presence of alamethicin, ATP-dependent enzyme activity interfered with the onset of inhibition. The transition of the enzyme between ouabain-sensitive and ATP-hydrolytic conformations consequently causes the non-linear concentration-dependence of pseudo-first-order rate constants. As the Hill coefficient was less than 1, a reaction of ouabain with two receptors also could have contributed to the special concentration-dependence of inhibition rates.
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Affiliation(s)
- F Ebner
- Institut für Pharmakologie und Toxikologie, Technischen Universität, München, Federal Republic of Germany
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39
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Skou JC. The fourth Datta lecture. The energy coupled exchange of Na+ for K+ across the cell membrane. The Na+, K(+)-pump. FEBS Lett 1990; 268:314-24. [PMID: 2166689 DOI: 10.1016/0014-5793(90)81278-v] [Citation(s) in RCA: 91] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- J C Skou
- Institute of Biophysics, University of Arhus, Denmark
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40
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de Moraes VL. Dimethyl sulfoxide: a possible effect on the interconversion of phosphorylated forms of Na+,K(+)-ATPase. BIOCHIMICA ET BIOPHYSICA ACTA 1990; 1026:135-40. [PMID: 2165812 DOI: 10.1016/0005-2736(90)90055-s] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Purified Na+,K(+)-ATPase from kidney outer medulla was phosphorylated by Pi in a reaction synergistically stimulated by Mg2+, when 40% (v/v) dimethyl sulfoxide was added to the assay medium. The phosphoenzyme formed at this solvent concentration was able to synthesize ATP even in the presence of Mg2+, because hydrolysis was impaired. ATP in equilibrium [32P]Pi exchange was also inhibited, indicating that partial reactions in the forward direction were blocked by the solvent. In 40% (v/v) dimethyl sulfoxide the enzyme's affinity for ADP decreased, in comparison with the values observed in purely aqueous medium. Addition of K+, which accelerated dephosphorylation of Na+,K(+)-ATPase in a totally water medium, partially reversed the inhibition of hydrolysis that was observed in the presence of dimethyl sulfoxide.
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Affiliation(s)
- V L de Moraes
- Departamento de Bioquímica, ICB, Universidade Federal de Rio de Janeiro, Brasil
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41
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Cornelius F. Variable stoichiometry in reconstituted shark Na,K-ATPase engaged in uncoupled efflux. BIOCHIMICA ET BIOPHYSICA ACTA 1990; 1026:147-52. [PMID: 2165814 DOI: 10.1016/0005-2736(90)90057-u] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
In liposomes with reconstituted shark Na,K-ATPase produced to contain no internal K+ or Na+ addition of external Na+ and ATP induce an uncoupled Na+ efflux on inside-out oriented pumps which is electrogenic and accompanied by hydrolysis of ATP (Cornelius, F. (1989) Biochem. Biophys. Res. Commun. 160, 801-807). At saturating cytoplasmic Na+ the net-charge translocated per ATP molecule split is compatible with a coupling ratio of Nacyt transported per ATP split of 3:1 at pH greater than or equal to 7.0. However, this ratio decreases to 1.5:1 below pH 7.0. At non-saturating cytoplasmic Na+ the 3:1 stoichiometry is attained at pH 7.0-7.5, whereas outside this range of pH the net-charge translocated per ATP molecule split decreases.
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Affiliation(s)
- F Cornelius
- Institute of Biophysics, University of Aarhus, Denmark
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42
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Abstract
The red cell Na/K pump is known to continue to extrude Na when both Na and K are removed from the external medium. Because this ouabain-sensitive flux occurs in the absence of an exchangeable cation, it is referred to as uncoupled Na efflux. This flux is also known to be inhibited by 5 mM Nao but to a lesser extent than that inhibitable by ouabain. Uncoupled Na efflux via the Na/K pump therefore can be divided into a Nao-sensitive and Nao-insensitive component. We used DIDS-treated, SO4-equilibrated human red blood cells suspended in HEPES-buffered (pHo 7.4) MgSO4 or (Tris)2SO4, in which we measured 22Na efflux, 35SO4 efflux, and changes in the membrane potential with the fluorescent dye, diS-C3 (5). A principal finding is that uncoupled Na efflux occurs electroneurally, in contrast to the pump's normal electrogenic operation when exchanging Nai for Ko. This electroneutral uncoupled efflux of Na was found to be balanced by an efflux of cellular anions. (We were unable to detect any ouabain-sensitive uptake of protons, measured in an unbuffered medium at pH 7.4 with a Radiometer pH-STAT.) The Nao-sensitive efflux of Nai was found to be 1.95 +/- 0.10 times the Nao-sensitive efflux of (SO4)i, indicating that the stoichiometry of this cotransport is two Na+ per SO4=, accounting for 60-80% of the electroneutral Na efflux. The remainder portion, that is, the ouabain-sensitive Nao-insensitive component, has been identified as PO4-coupled Na transport and is the subject of a separate paper. That uncoupled Na efflux occurs as a cotransport with anions is supported by the result, obtained with resealed ghosts, that when internal and external SO4 was substituted by the impermeant anion, tartrate i,o, the efflux of Na was inhibited 60-80%. This inhibition could be relieved by the inclusion, before DIDS treatment, of 5 mM Cli,o. Addition of 10 mM Ko to tartrate i,o ghosts, with or without Cli,o, resulted in full activation of Na/K exchange and the pump's electrogenicity. Although it can be concluded that Na efflux in the uncoupled mode occurs by means of a cotransport with cellular anions, the molecular basis for this change in the internal charge structure of the pump and its change in ion selectivity is at present unknown.
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Affiliation(s)
- S Dissing
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510
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43
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Blatt MR, Beilby MJ, Tester M. Voltage dependence of the Chara proton pump revealed by current-voltage measurement during rapid metabolic blockade with cyanide. J Membr Biol 1990; 114:205-23. [PMID: 2157844 DOI: 10.1007/bf01869215] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
It is generally agreed that solute transport across the Chara plasma membrane is energized by a proton electrochemical gradient maintained by an H(+)-extruding ATPase. Nonetheless, as deduced from steady-state current-voltage (I-V) measurements, the kinetic and thermodynamic constraints on H(+)-ATPase function remain in dispute. Uncertainties necessarily surround long-term effects of the relatively nonspecific antagonists used in the past; but a second, and potentially more serious problem has sprung from the custom of subtracting, across the voltage spectrum, currents recorded following pump inhibition from currents measured in the control. This practice must fail to yield the true I-V profile for the pump when treatments alter the thermodynamic pressure on transport. We have reviewed these issues, using rapid metabolic blockade with cyanide and fitting the resultant whole-cell I-V and difference-current-voltage (dI-V) relations to a reaction kinetic model for the pump and parallel, ensemble leak. Measurements were carried out after blocking excitation with LaCl3, so that steady-state currents could be recorded under voltage clamp between -400 and +100 mV. Exposures to 1 mM NaCN (CN) and 0.4 mM salicylhydroxamic acid (SHAM) depolarized (positive-going) Chara membrane potentials by 44-112 mV with a mean half time of 5.4 +/- 0.8 sec (n = 13). ATP contents, which were followed in parallel experiments, decayed coincidently with a mean half time of 5.3 +/- 0.9 sec [( ATP]t = 0, 0.74 +/- 0.3 mM; [ATP]t = infinity, 0.23 +/- 0.02 mM). Current-voltage response to metabolic blockade was described quantitatively in context of these changes in ATP content and the consequent reduction in pump turnover rate accompanied by variable declines in ensemble leak conductance. Analyses of dI-V curves (+/- CN + SHAM) as well as of families of I-V curves taken at times during CN + SHAM exposures indicated a stoichiometry for the pump of one charge (H+) transported per ATP hydrolyzed and an equilibrium potential near -420 mV at neutral external pH; under these conditions, the pump accounted for approximately 60-75% of the total membrane conductance near Vm. Complementary results were obtained also in fitting previously published I-V data gathered over the external pH range 4.5-7.5. Kinetic features deduced for the pump were dominated by a slow step preceding H+ unloading outside, and by recycling and loading steps on the inside which were in rapid equilibrium.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- M R Blatt
- Botany School, University of Cambridge, England
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44
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Guerra M, Robinson JD, Steinberg M. Differential effects of substrates on three transport modes of the Na+/K(+)-ATPase. BIOCHIMICA ET BIOPHYSICA ACTA 1990; 1023:73-80. [PMID: 2156564 DOI: 10.1016/0005-2736(90)90011-c] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
With a purified Na+/K(+)-ATPase preparation reconstituted into phospholipid vesicles, Na+/K+, Na+/Na+, and uncoupled Na+ transport were studied using three nucleotides and five substrates of the K(+)-phosphatase reaction that this enzyme also catalyzes. For Na+/K+ exchange, CTP was half as effective as ATP and GTP one-twentieth; of the phosphatase substrates only carbamyl phosphate and 3-O-methylfluorescein phosphate produced significant transport and at merely 1% of the rate with ATP. For Na+/Na+ exchange, comparable rates of transport were produced by ATP, CTP, carbamyl phosphate and acetyl phosphate, although the actual rate of transport with ATP was only 2.4% of that for Na+/K+ exchange; slower rates occurred with GTP (69%), 3-O-methylfluorescein phosphate (51%), and nitrophenyl phosphate (33%). Only umbelliferone phosphate was ineffective. For uncoupled Na+ transport results similar to those for Na+/Na+ exchange were obtained, but the actual rate of transport was still slower, 1.4% of that for Na+/K+ exchange. Thus, not only nucleotides but a variety of phosphatase substrates (which are phosphoric acid mixed anhydrides) can phosphorylate the enzyme at the high-affinity substrate site to form the E1P intermediate of the reaction sequence. Oligomycin inhibited Na+/K+ exchange with ATP by half, but with carbamyl phosphate not at all; with CTP the inhibition was intermediate, one-fourth. By contrast, oligomycin inhibited Na+/Na+ exchange by one-fifth with all three substrates. A quantitative, steady-state kinetic model accounts for the relative magnitudes of Na+/K+ and Na+/Na+ exchanges with ATP, CTP, and carbamyl phosphate as substrates, as well as the extents of inhibition by oligomycin. The model requires that even when Na+ substitutes for K+ a slow step in the reaction sequence is the E2 to E1 conformational transition.
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Affiliation(s)
- M Guerra
- Department of Pharmacology, SUNY Health Science Center, Syracuse 13210
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45
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Takada J, Hioki Y, Yano M, Fukushima Y. A novel hydrophobic amine, (Z)-5-methyl-2-[2-(1-naphthyl)ethenyl]-4-piperidinopyridine, as a probe of the K+ occlusion center of Na+/K(+)-ATPase. BIOCHIMICA ET BIOPHYSICA ACTA 1990; 1037:373-9. [PMID: 2155657 DOI: 10.1016/0167-4838(90)90039-i] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
A hydrophobic amine, (Z)-5-methyl-2-[2-(1-naphthyl)ethenyl]-4-piperidinopyridine (AU-1421), was examined as a probe of the K+ occlusion center of Na+/K(+)-ATPase. Treatment of the enzyme with AU-1421 at 37 degrees C and pH 7.0 produced irreversible inactivation of the enzyme. This inactivation was prevented, with simple competitive kinetics, by K+ or its congeners in the order of Tl+ greater than Rb+ greater than NH+4 greater than Cs+. The concentrations of these cations required for the protection, were consistent with the affinities for transport and ATPase activity. The apparent binding constant for K+ was calculated to be 0.03 mM, from the competition with AU-1421. This protection was cancelled by a high concentration of ATP or ADP. A high concentration of Na+ (Kd = 6.5-6.9 mM), as a substitute for K+, also prevented the inactivation by AU-1421. Thus, the enzyme was protected from AU-1421 when the occlusion center was occupied by a monovalent cation, irrespective of the enzyme conformation, E1 (Na(+)-bound form) or E2 (K(+)-bound form). On the other hand, the enzyme was most sensitive to AU-1421 in the presence of low concentration of Na+ (0.4-0.8 mM) or a high concentration of ATP. Tris, imidazole or choline, which favors the E1 state, also accelerated the inactivation by AU-1421. These suggest that AU-1421 reacts with the occlusion center through the E1 state.
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Affiliation(s)
- J Takada
- Central Research Laboratories, Banyu Pharmaceutical Co., Tokyo, Japan
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46
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Stürmer W, Apell HJ, Wuddel I, Läuger P. Conformational transitions and change translocation by the Na,K pump: comparison of optical and electrical transients elicited by ATP-concentration jumps. J Membr Biol 1989; 110:67-86. [PMID: 2552127 DOI: 10.1007/bf01870994] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The electrogenic properties of the Na,K-ATPase were studied by correlating transient electrical events in the pump molecule with conformational transitions elicited by an ATP-concentration jump. Flat membrane fragments containing a high density (approximately 8000 microm(-2)) of oriented Na,K-ATPase molecules were bound to a planar lipid bilayer acting as a capacitive electrode. ATP was released in the medium from a photolabile inactive ATP derivative ("caged" ATP) by a 40-microsec light flash. Electrical signals resulting from transient charge movements in the protein under single-turnover conditions were recorded in the external measuring circuit. In parallel experiments carried out under virtually identical conditions, the fluorescence of membrane fragments containing Na,K-ATPase with covalently-bound 5-iodoacetamido-fluorescein (5-IAF) was monitored after the ATP-concentration jump. When the medium contained Na+, but no K+, the fluorescence of the 5-IAF-labeled protein decreases monotonously after release of ATP. In the experiments with membrane fragments bound to a planar bilayer, a transient pump current was observed which exhibited virtually the same time behavior as the fluorescence decay. This indicates that optical and electrical transients are governed by the same rate-limiting reaction step. Experiments with chymotrypsin-modified Na,K-ATPase suggest that both the fluorescence change as well as the charge movement are associated with the deocclusion of Na+ and release to the extracellular side. In experiments with Na+-free K+ media, a large inverse fluorescence change is observed after the ATP-concentration jump, but no charge translocation can be detected. This indicates that deocclusion of K+ is an electrically silent process.
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Affiliation(s)
- W Stürmer
- Department of Biology, University of Konstanz, Federal Republic of Germany
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47
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Abstract
In liposomes with reconstituted shark Na,K-ATPase produced to contain sucrose addition of external Na+ and ATP induce an uncoupled Na+-efflux on inside-out oriented pumps which can be inhibited by digitoxigenin. This flux mode is found to be electrogenic and accompanied by hydrolysis of ATP. The coupling ratio of Nacyt transported per ATP split is 3:1 measured as the initial rate of rise in transmembrane potential and initial rate of liberated Pi.
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Affiliation(s)
- F Cornelius
- Institute of Biophysics, University of Aarhus, Denmark
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48
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Steinberg M, Karlish SJ. Studies on conformational changes in Na,K-ATPase labeled with 5-iodoacetamidofluorescein. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(19)81673-3] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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49
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Tyson PA, Steinberg M, Wallick ET, Kirley TL. Identification of the 5-Iodoacetamidofluorescein Reporter Site on the Na,K-ATPase. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(19)85003-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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50
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Shani-Sekler M, Goldshleger R, Tal DM, Karlish SJ. Inactivation of Rb+ and Na+ occlusion on (Na+,K+)-ATPase by modification of carboxyl groups. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(19)77638-8] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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