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Jaeken L, Vasilievich Matveev V. Coherent Behavior and the Bound State of Water and K(+) Imply Another Model of Bioenergetics: Negative Entropy Instead of High-energy Bonds. Open Biochem J 2012; 6:139-59. [PMID: 23264833 PMCID: PMC3527877 DOI: 10.2174/1874091x01206010139] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2012] [Revised: 09/06/2012] [Accepted: 09/12/2012] [Indexed: 11/22/2022] Open
Abstract
Observations of coherent cellular behavior cannot be integrated into widely accepted membrane (pump) theory (MT) and its steady state energetics because of the thermal noise of assumed ordinary cell water and freely soluble cytoplasmic K(+). However, Ling disproved MT and proposed an alternative based on coherence, showing that rest (R) and action (A) are two different phases of protoplasm with different energy levels. The R-state is a coherent metastable low-entropy state as water and K(+) are bound to unfolded proteins. The A-state is the higher-entropy state because water and K(+) are free. The R-to-A phase transition is regarded as a mechanism to release energy for biological work, replacing the classical concept of high-energy bonds. Subsequent inactivation during the endergonic A-to-R phase transition needs an input of metabolic energy to restore the low entropy R-state. Matveev's native aggregation hypothesis allows to integrate the energetic details of globular proteins into this view.
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Affiliation(s)
- Laurent Jaeken
- Laboratory of Biochemistry, Karel de Grote University College, Department of Applied Engineering, Salesianenlaan 30, B-2660, Antwerp, Belgium
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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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Repke KR, Schön R. Synthesis of a self-contained concept of the molecular mechanism of energy interconversion by H(+)-transporting ATP synthase. Biol Rev Camb Philos Soc 1994; 69:119-45. [PMID: 8054442 DOI: 10.1111/j.1469-185x.1994.tb01503.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The original aim of the review has been to probe into the validity of the paradigm on the high energy-carrier function of ATP. It seemed to be called into question on the basis of findings with H(+)-transporting ATP synthase suggesting the formation of ATP from ADP and Pi without energy input. Thus, ATP appeared as a low-energy compound. Starting from the current, rich knowledge of the molecular structure and the inviting thinking on the mechanism of H(+)-transporting ATP synthase, we have endeavoured to freshly interpret and integrate the pertinent observations in the light of the comprehensively derived model of the molecular mechanism of energy interconversion by Na+/K(+)-transporting ATPase. In this way, we have uncovered the common mechanistic elements of the two energy-interconverting enzymes. The emerging purpose of the present paper has been the 'synthesis' of a self-contained concept of the molecular mechanism of the interconversion of electrochemical and chemical Gibbs energies by H(+)-transporting ATP synthase. The outcome is reflected in the following tentative evaluations. 1. In ATP hydrolysis, the great Gibbs energy change which is observed in solution, is largely conserved by the F1 sector of ATP synthase as mechanical Gibbs energy in the enzyme's protein fabric, so that it can be utilized in the resynthesis of ATP from enzyme-bound ADP and Pi. The plainly measured low Gibbs energy change results from large compensating enthalpy and entropy changes that reflect the underlying changes in protein conformation. 2. In stoichiometric ATP synthesis by F1 sector from ADP and Pi bound to the catalytic centre, their intrinsic binding energy brings about a loss of peptide chain entropy that makes possible an entropy-driven ATP formation. 3. The driving force for ATP synthesis cannot be the high Gibbs energy change on binding of product ATP; the tight ATP-enzyme complex rather is a low Gibbs energy intermediate from which escape is difficult. 4. The catalytic centre exists either in an open state unable to firmly bind the substrate-product couple, or in a closed state protecting formed ATP from facile hydrolysis by ambient water. 5. The cleft closure, induced by binding of Pi and ADP or ATP, does not necessarily need external energy supply, because the cleft closure proceeds from rigid domain rotations which can occur rather spontaneously. In further analogy to adenylate kinase, the driving force of this domain movement presumably comes from the electrostatic interactions between phosphate moieties and arginine side chains in the catalytic centre.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- K R Repke
- Energy Conversion Unit, Max Delbrück Centre for Molecular Medicine, Berlin-Buch, Germany
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Repke KR, Schön R. Chemistry and energetics of transphosphorylations in the mechanism of Na+/K(+)-transporting ATPase: an attempt at a unifying model. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1154:1-16. [PMID: 8389589 DOI: 10.1016/0304-4157(93)90014-f] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- K R Repke
- Energy Conversion Unit, Max Delbrück Centre for Molecular Medicine, Berlin-Buch, Germany
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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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Plesner L, Karlsmose B, Lüscher ME. [32P]ATP synthesis in steady state from [32P]Pi and ADP by Na+/K(+)-ATPase from ox brain and pig kidney. Activation by K+. BIOCHIMICA ET BIOPHYSICA ACTA 1990; 1040:167-74. [PMID: 2169305 DOI: 10.1016/0167-4838(90)90072-n] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The ouabain-sensitive synthesis of [32P]ATP from [32P]Pi and ADP (vsyn) was measured in parallel with the ouabain-sensitive hydrolysis of [32P]ATP (vhy) at steady state, at varying concentrations of sodium, potassium, magnesium, inorganic phosphate, ADP, ATP and oligomycin, and at varying pH. Na+ was necessary for ATP synthesis, but vsyn was decreased by high sodium concentrations. Oligomycin, depending on the Na+ concentration, either decreased or did not affect vsyn. Potassium, at low concentrations (1-5 mM) increased vsyn at all magnesium and sodium concentrations tested, lower potassium concentrations being needed to activate vsyn at lower sodium concentrations. vsyn was optimal below pH 6.7, decreasing abruptly at higher values of pH. At pH 6.7, vsyn was a hyperbolic function of the concentration of inorganic phosphate. In the presence of potassium, half-maximal rate was obtained at [Pi] congruent to 40 mM, whereas a higher concentration was needed to obtain half-maximal rate in the absence of K+. In contrast, increasing the concentration of ADP caused a nonhyperbolic activation of vsyn, the pattern obtained in the presence of potassium being different from that obtained in its absence. Increasing the ATP concentration above 0.5 mM decreased vsyn. The data are used to elucidate (1) which reaction steps are involved in the ATP-synthesis catalysed by the Na+/K(+)-ATPase at steady state in the absence of ionic gradients and (2) the mechanism by which K+ ions stimulate the reaction.
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Affiliation(s)
- L Plesner
- Institute of Biophysics, University of Aarhus, Denmark
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7
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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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8
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de Meis L. Role of water in the energy of hydrolysis of phosphate compounds--energy transduction in biological membranes. BIOCHIMICA ET BIOPHYSICA ACTA 1989; 973:333-49. [PMID: 2537102 DOI: 10.1016/s0005-2728(89)80440-2] [Citation(s) in RCA: 131] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- L de Meis
- Departamento de Bioquimica, Universidade Federal do Rio de Janeiro, Brazil
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9
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Selective inhibition by ionophore A23187 of the enzyme isomerization in the catalytic cycle of Na+, K+ -ATPase. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)69052-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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10
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de Moraes VL, de Meis L. ATP synthesis by the (Na+ + K+)-ATPase in the absence of an ionic gradient. Effects of organic solvent. FEBS Lett 1987; 222:163-6. [PMID: 2820794 DOI: 10.1016/0014-5793(87)80212-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
A 200-fold decrease in the Pi concentration required for half-maximal phosphorylation of the (Na+ + K+)-ATPase is observed when 40% (v/v) dimethyl sulfoxide is added to the assay medium. The phosphoenzyme formed in the presence of dimethyl sulfoxide is able to transfer its phosphate to to form ATP when concentrations of organic solvent and of Na+, and is inhibited by ouabain.
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Affiliation(s)
- V L de Moraes
- Departamento de Bioquimica, Universidade Federal do Rio de Janeiro, Ilha do Fundao, Brazil
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11
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12
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Huang WH, Kakar SS, Askari A. Mechanisms of detergent effects on membrane-bound (Na+ + K+)-ATPase. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(17)39616-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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13
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Taniguchi K, Suzuki K, Kai D, Matsuoka I, Tomita K, Iida S. Conformational change of sodium- and potassium-dependent adenosine triphosphatase. Conformational evidence for the Post-Albers mechanism in Na+- and K+-dependent hydrolysis of ATP. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(17)42539-7] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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14
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Gonçalves de Moraes VL, De Meis L. Exchange between inorganic phosphate and adenosine triphosphate in (Na+,K+)-ATPase. BIOCHIMICA ET BIOPHYSICA ACTA 1982; 688:131-7. [PMID: 6284227 DOI: 10.1016/0005-2736(82)90587-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
(Na+,K+)-ATPase is able to catalyze a continuous ATP in equilibrium Pi exchange in the presence of Na+ and in the absence of a transmembrane ionic gradient. At pH 7.6 the Na+ concentration required for half-maximal activity is 85 mM and at pH 5.1 it is 340 mM. In the presence of optimal Na+ concentration, the rate of exchange is maximal at pH 6.0 and varies with ADP and Pi concentration in the assay medium. ATP in equilibrium Pi exchange is inhibited by K+ and by ouabain.
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15
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Gradmann D, Hansen UP, Sla Yman CL. Chapter 14 Reaction-Kinetic Analysis of Current-Voltage Relationships for Electrogenic Pumps in Neurospora and Acetabularia. CURRENT TOPICS IN MEMBRANES AND TRANSPORT 1982. [DOI: 10.1016/s0070-2161(08)60704-2] [Citation(s) in RCA: 35] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
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Flatman PW, Lew VL. The magnesium dependence of sodium-pump-mediated sodium-potassium and sodium-sodium exchange in intact human red cells. J Physiol 1981; 315:421-46. [PMID: 6796677 PMCID: PMC1249391 DOI: 10.1113/jphysiol.1981.sp013756] [Citation(s) in RCA: 68] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
1. The magnesium content of human red blood cells was controlled by varying the magnesium concentration in the medium in the presence of the ionophore A23187. The new magnesium levels attained were very stable, which allowed the magnesium dependence of the sodium pump to be investigated.2. The effects of magnesium were shown to occur at the inner surface of the red cell membrane for the range of magnesium concentrations tested (10(-7) to 6 x 10(-3)m).3. At intracellular ionized magnesium concentrations below 0.8 mm the activation of ouabain-sensitive sodium-potassium exchange by internal ionized magnesium could be resolved into two or three components: (a) a small component, about 5% of the maximum flux, which is apparently independent of the ionized magnesium concentration below 2 mum, (b) a saturating component with a K((1/2)) of between 30 and 45 mum, and possibly (c) a component which increases linearly with ionized magnesium concentration and which only becomes apparent at concentrations above 0.1 mm.4. At intracellular ionized magnesium concentrations below 0.8 mm, activation of ouabain-sensitive sodium-sodium exchange by internal ionized magnesium could be resolved into two components: (a) a small component, about 6% of the maximal flux, which is apparently independent of the ionized magnesium concentration below 2 mum, and (b) a saturating component with a K((1/2)) of about 9 mum. At ionized magnesium concentrations between about 0.2 and 0.8 mm the rate of sodium-sodium exchange remained constant at the maximal level.5. The intracellular concentration of ATP decreased and the ADP concentration increased as the magnesium content of the cells was reduced from the normal level. A small increase in ATP and a small decrease in ADP was seen when the magnesium content was increased above the normal level. The variation in the ATP: ADP ratio from 2.5 at very low magnesium levels to about 6 at normal magnesium levels can account, at least in part, for the different K((1/2)) values of sodium-potassium and sodium-sodium exchange.6. When the concentration of ionized magnesium was increased above about 0.8 mm both sodium-potassium and sodium-sodium exchange were inhibited. Sodium-sodium exchange was more strongly inhibited than sodium-potassium exchange.7. The possible sites of action of magnesium in the sodium pump cycle are discussed.
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Klodos I, Nørby JG, Plesner IW. The steady-state kinetic mechanism of ATP hydrolysis catalyzed by membrane-bound (Na+ + K+)-ATPase from ox brain. II. Kinetic characterization of phosphointermediates. BIOCHIMICA ET BIOPHYSICA ACTA 1981; 643:463-82. [PMID: 6261817 DOI: 10.1016/0005-2736(81)90089-4] [Citation(s) in RCA: 40] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
(1) The kinetics of the phosphorylated enzymic intermediates of (Na+ + K+)-ATPase from ox brain, which are formed by incubation of the enzyme with 25 microM AT32P, 150 mM Na+ and 1 mM Mg2+, have been studied in dephosphorylation experiments at 1 degree C. The dephosphorylation of the 32P-labelled enzyme was initiated by addition of either 1 mM unlabelled ATP, 2.5 mM ADP or 1 mM unlabelled ATP + ADP in concentrations from 25 to 1000 microM. (2) In the absence of ADP the dephosphorylation curve was linear in a semilogarithmic plot almost from t = 0, whereas by addition of ADP a biphasic behaviour was obtained. The slope of the slow phase of dephosphorylation was virtually independent of the ADP concentration. (3) The results were analysed by the mathematical equation corresponding to the simplest possible model for the interconversion and breakdown of the phosphointermediates: (formula: see text) where alpha, beta, H and G are functions of all the rate constants and H and G furthermore are functions of the initial values for [E1P] and [E2P]. (4) The analysis confirmed the model and enabled the determination of all the rate constants. (5) k-1 was found to be equal to k'-1 + k"-1 . [ADP] indicating an ADP-independent 'spontaneous' dephosphorylation of E1P. The rate constant for this process was close to that for dephosphorylation of E2P, i.e., k'-1 congruent to k3. Also the value of k"-1 was determined. (6) k3 was found to be at least 10 . k-2. The implication of this for the role of the E1P to E2P transition in the Na+ + K+)-stimulated ATP hydrolysis will be discussed in detail in the following paper (Plesner, I.W., Plesner, L., Nørby, J.G. and Klodos, I. (1981) Biochim. Biophys. Acta 643, 483--494). (7) A refinement of the model, accounting for the effect of Na+ on the steady-state ratio between [E1P] and [E2P] is proposed: (formula: see text). At [Na+] = 150 mM as used here, E1P(Na) and E'1P are assumed to be in rapid equilibrium. (8) Comparison of our results with those of others underlines the general validity of the conclusions of the present paper.
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Inhibition of sodium and potassium adenosine triphosphatase by 2‘,3‘-O-(2,4,6-trinitrocyclohexadienylidene) adenine nucleotides. Implications for the structure and mechanism of the Na:K pump. J Biol Chem 1981. [DOI: 10.1016/s0021-9258(19)69787-5] [Citation(s) in RCA: 118] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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Flatman PW, Lew VL. Excess magnesium converts red cell (sodium+potassium) ATPase to the potassium phosphatase. J Physiol 1980; 307:1-8. [PMID: 6259330 PMCID: PMC1283029 DOI: 10.1113/jphysiol.1980.sp013419] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
1. The ATPase and phosphatase activities of red cell membranes were measured simultaneously as a function of the magnesium content of the medium. 2. It was found that when the magnesium concentration was greater than that of ATP, magnesium inhibited the ATPase and simultaneously stimulated the phosphatase. The concentrations of magnesium needed for half-maximal stimulation of the phosphatase and half-maximal inhibition of the ATPase were similar. 3. It is suggested that increasing the concentration of magnesium directly causes a change in the conformation of the enzyme from one which favours ATPase activity to one which favours phosphatase activity.
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Fukushima Y, Nakao M. Changes in affinity of Na+- and K+-transport ATPase for divalent cations during its reaction sequence. J Biol Chem 1980. [DOI: 10.1016/s0021-9258(19)43905-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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Fukushima Y, Post R. Binding of divalent cation to phosphoenzyme of sodium- and potassium-transport adenosine triphosphatase. J Biol Chem 1978. [DOI: 10.1016/s0021-9258(17)37998-x] [Citation(s) in RCA: 82] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Karlish SJ, Yates DW, Glynn IM. Conformational transitions between Na+-bound and K+-bound forms of (Na+ + K+)-ATPase, studied with formycin nucleotides. BIOCHIMICA ET BIOPHYSICA ACTA 1978; 525:252-64. [PMID: 210812 DOI: 10.1016/0005-2744(78)90219-x] [Citation(s) in RCA: 215] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
1. Fluorescence measurements have shown that formycin triphosphate (FTP) or formycin diphosphate (FDP) bound to (Na+ + K+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) in Na+-containing media can be displaced by the following ions (listed in order of effectiveness): Tl+, K+, Rb+, NH4+, Cs+. 2. The differences between the nucleotide affinities displayed by the enzyme in predominantly Na+ and predominantly K+ media in the absence of phosphorylation, are thought to reflect changes in enzyme conformation. These changes can therefore be monitored by observing the changes in fluorescence that accompany net binding or net release of formycin nucleotides. 3. The transition from a K+-bound form (E2-(K)) to an Na+-bound form (E1-Na) is remarkably slow at low nucleotide concentrations, but is accelerated if the nucleotide concentration is increased. This suggests that the binding of nucleotide to a low-affinity site on E2-(K) accelerates its conversion to E1-Na; it supports the hypothesis that during the normal working of the pump, ATP, acting at a low affinity site, accelerates the conversion of dephosphoenzyme, newly formed by K+-catalysed hydrolysis of E2P, to a form in which it can be phosphorylated in the presence of Na+. 4. The rate of the reverse transformation, E1-Na to E2-(K), varies roughly linearly with the K+ concentration up to the highest concentration at which the rate can be measured (15 mM). Since much lower concentrations of K+ are sufficient to displace the equilibrium to the K-form, we suggest that the sequence of events is: (i) combination of K+ with low affinity (probably internal) binding sites, followed by (ii) spontaneous conversion of the enzyme to a form, E2-(K), containing occluded K+. 5. Mg2+ or oligomycin slows the rate of conversion of E1-Na to E2-(K) but does not significantly affect the rate of conversion of E2-(K) to E1-Na. 6. In the light of these and previous findings, we propose a model for the sodium pump in which conformational changes alternate with trans-phosphorylations, and the inward and outward fluxes of both Na+ and K+ each involve the transfer of a phosphoryl group as well as a change in conformation between E1 and E2 forms of the enzyme or phosphoenzyme.
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