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Saffioti NA, de Sautu M, Ferreira-Gomes MS, Rossi RC, Berlin J, Rossi JPFC, Mangialavori IC. E2P-like states of plasma membrane Ca 2+‑ATPase characterization of vanadate and fluoride-stabilized phosphoenzyme analogues. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1861:366-379. [PMID: 30419189 DOI: 10.1016/j.bbamem.2018.11.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 06/18/2018] [Revised: 10/22/2018] [Accepted: 11/01/2018] [Indexed: 01/18/2023]
Abstract
The plasma membrane Ca2+‑ATPase (PMCA) belongs to the family of P-type ATPases, which share the formation of an acid-stable phosphorylated intermediate as part of their reaction cycle. The crystal structure of PMCA is currently lacking. Its abundance is approximately 0.1% of the total protein in the membrane, hampering efforts to produce suitable crystals for X-ray structure analysis. In this work we characterized the effect of beryllium fluoride (BeFx), aluminium fluoride (AlFx) and magnesium fluoride (MgFx) on PMCA. These compounds are known inhibitors of P-type ATPases that stabilize E2P ground, E2·P phosphoryl transition and E2·Pi product states. Our results show that the phosphate analogues BeFx, AlFx and MgFx inhibit PMCA Ca2+‑ATPase activity, phosphatase activity and phosphorylation with high apparent affinity. Ca2+‑ATPase inhibition by AlFx and BeFx depended on Mg2+ concentration indicating that this ion stabilizes the complex between these inhibitors and the enzyme. Low pH increases AlFx and BeFx but not MgFx apparent affinity. Eosin fluorescent probe binds with high affinity to the nucleotide binding site of PMCA. The fluorescence of eosin decreases when fluoride complexes bind to PMCA indicating that the environment of the nucleotide binding site is less hydrophobic in E2P-like states. Finally, measuring the time course of E → E2P-like conformational change, we proposed a kinetic model for the binding of fluoride complexes and vanadate to PMCA. In summary, our results show that these fluoride complexes reveal different states of phosphorylated intermediates belonging to the mechanism of hydrolysis of ATP by the PMCA.
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Affiliation(s)
- Nicolás A Saffioti
- Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Instituto de Química y Fisicoquímica Biológicas (IQUIFIB), Facultad de Farmacia y Bioquímica, Junín 956, Ciudad Autónoma de Buenos Aires C1113AAD, Argentina
| | - Marilina de Sautu
- Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Instituto de Química y Fisicoquímica Biológicas (IQUIFIB), Facultad de Farmacia y Bioquímica, Junín 956, Ciudad Autónoma de Buenos Aires C1113AAD, Argentina
| | - Mariela S Ferreira-Gomes
- Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Instituto de Química y Fisicoquímica Biológicas (IQUIFIB), Facultad de Farmacia y Bioquímica, Junín 956, Ciudad Autónoma de Buenos Aires C1113AAD, Argentina
| | - Rolando C Rossi
- Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Instituto de Química y Fisicoquímica Biológicas (IQUIFIB), Facultad de Farmacia y Bioquímica, Junín 956, Ciudad Autónoma de Buenos Aires C1113AAD, Argentina
| | - Joshua Berlin
- Department of Pharmacology and Physiology, New Jersey Medical School, Rutgers University, Newark, NJ, USA
| | - Juan Pablo F C Rossi
- Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Instituto de Química y Fisicoquímica Biológicas (IQUIFIB), Facultad de Farmacia y Bioquímica, Junín 956, Ciudad Autónoma de Buenos Aires C1113AAD, Argentina
| | - Irene C Mangialavori
- Universidad de Buenos Aires, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Instituto de Química y Fisicoquímica Biológicas (IQUIFIB), Facultad de Farmacia y Bioquímica, Junín 956, Ciudad Autónoma de Buenos Aires C1113AAD, Argentina.
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Plenge-Tellechea F, Domínguez-Solís CA, Díaz-Sánchez ÁG, Meléndez-Martínez D, Vargas-Medrano J, Sierra-Fonseca JA. Chlorpromazine and dimethyl sulfoxide modulate the catalytic activity of the plasma membrane Ca 2+-ATPase from human erythrocyte. J Bioenerg Biomembr 2018; 50:59-69. [PMID: 29313294 DOI: 10.1007/s10863-017-9741-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2017] [Accepted: 12/28/2017] [Indexed: 01/03/2023]
Abstract
The plasma membrane Ca2+-ATPase (PMCA) removes Ca2+ from the cytosol into the extracellular space. Its catalytic activity can be stimulated by calmodulin (CaM) or by limited proteolysis. We evaluated the effect of chlorpromazine (CPZ) and dimethyl sulfoxide (DMSO) over the hydrolytic activity of PMCA. Activity was monitored in three different forms: native, CaM-activated and proteolyzed by trypsin. CPZ appears to inhibit PMCA without directly interfering with the C-terminal site, since it is affected by CaM and proteolysis. Although the treatment of PMCA with trypsin and CaM produces an activation, it also produces an enzymatic form that is more sensitive to inhibition by CPZ. The same case was observed in the DMSO inhibition experiments. In the absence of CPZ, DMSO produces a progressive loss of activity, but in the presence of CPZ the profile of activity against DMSO changes and produces a recovery of activity, indicating a possible partition of CPZ by the solvent. Increasing Ca2+ concentrations indicated that CPZ interacts with PMCA rather than with CaM. This observation is supported by docking analysis that suggests that the CPZ-PMCA interaction is non-competitive. We propose that CPZ interacts with the state of lower affinity for Ca2 +.
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Affiliation(s)
- Fernando Plenge-Tellechea
- Laboratorio de Biología Molecular y Bioquímica (Edif. T-216), Departamento de Ciencias Químico-Biológicas, Instituto de Ciencias Biomédicas, Universidad Autónoma de Ciudad Juárez, C. P. 32310, Ciudad Juárez, CHI, Mexico. .,Departamento de Ciencias Químico-Biológicas, Instituto de Ciencias Biomédicas, Universidad Autónoma de Ciudad Juárez, Plutarco Elías Calles #1210, Fovissste Chamizal, Ciudad Juárez, C.P. 32310, Chihuahua, Mexico.
| | - Carlos A Domínguez-Solís
- Laboratorio de Biología Molecular y Bioquímica (Edif. T-216), Departamento de Ciencias Químico-Biológicas, Instituto de Ciencias Biomédicas, Universidad Autónoma de Ciudad Juárez, C. P. 32310, Ciudad Juárez, CHI, Mexico
| | - Ángel G Díaz-Sánchez
- Laboratorio de Biología Molecular y Bioquímica (Edif. T-216), Departamento de Ciencias Químico-Biológicas, Instituto de Ciencias Biomédicas, Universidad Autónoma de Ciudad Juárez, C. P. 32310, Ciudad Juárez, CHI, Mexico
| | - David Meléndez-Martínez
- Laboratorio de Biología Molecular y Bioquímica (Edif. T-216), Departamento de Ciencias Químico-Biológicas, Instituto de Ciencias Biomédicas, Universidad Autónoma de Ciudad Juárez, C. P. 32310, Ciudad Juárez, CHI, Mexico
| | - Javier Vargas-Medrano
- Laboratorio de Biología Molecular y Bioquímica (Edif. T-216), Departamento de Ciencias Químico-Biológicas, Instituto de Ciencias Biomédicas, Universidad Autónoma de Ciudad Juárez, C. P. 32310, Ciudad Juárez, CHI, Mexico.,Department of Biomedical Sciences, Center of Emphasis for Neurosciences, Texas Tech University Health Sciences Center, El Paso, TX, 79905, USA
| | - Jorge A Sierra-Fonseca
- Laboratorio de Biología Molecular y Bioquímica (Edif. T-216), Departamento de Ciencias Químico-Biológicas, Instituto de Ciencias Biomédicas, Universidad Autónoma de Ciudad Juárez, C. P. 32310, Ciudad Juárez, CHI, Mexico.,Department of Biological Sciences, University of Texas at El Paso, El Paso, TX, 79968, USA
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3
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Changes of Cell Membrane Permeability Induced by DMSO and Ethanol in Suspension Cultures of Taxus Cuspidata. ACTA ACUST UNITED AC 2011. [DOI: 10.4028/www.scientific.net/amr.236-238.942] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The changes of cell membrane permeability caused by dimethyl sulphoxide (DMSO) and ethanol, two commonly used solvents in study of water-insoluble elicitors, were investigated in suspension cultures of Taxus cuspidata. The extracellular medium became alkalinized in the case of DMSO while the medium pH fluctuated upon the addition of ethanol. When the content of DMSO or ethanol was larger than 2% (v/v), the concentration of intracellular malonyl dialdehyde (MDA) increased remarkably at day 5 compared to that of the control, while that of the extracellular MDA less changed at a DMSO content of below 2% (v/v) and increased rapidly within 15 min at a DMSO content of 4% (v/v). The electrical conductivity (EC) decreased slightly when DMSO content was below 2% (v/v) but increased markedly at day 5 when DMSO content reached 4% (v/v). EC less varied when the content of ethanol was below 0.4% (v/v) but changed obviously when the ethanol content was larger than 1% (v/v). The cell membrane integrity hardly broke in the case of small concentration of DMSO (below 1%, v/v), but the presence of even small amount of ethanol (0.4%, v/v) caused cell membrane integrity lost partly, especially long time contact. It is thus concluded that DMSO is a more suitable solvent for water-insoluble elicitors compared to ethanol especially at low concentration levels.
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Zemlyanskikh NG, Denisova ON. Changes in the erythrocyte membrane-cytoskeleton complex induced by dimethyl sulfoxide, polyethylene glycol, and low temperature. Biophysics (Nagoya-shi) 2009. [DOI: 10.1134/s0006350909040162] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Oliveira VH, Nascimento KSO, Freire MM, Moreira OC, Scofano HM, Barrabin H, Mignaco JA. Mechanism of modulation of the plasma membrane Ca(2+)-ATPase by arachidonic acid. Prostaglandins Other Lipid Mediat 2008; 87:47-53. [PMID: 18718873 DOI: 10.1016/j.prostaglandins.2008.07.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2007] [Revised: 07/15/2008] [Accepted: 07/22/2008] [Indexed: 10/25/2022]
Abstract
The intracellular level of long chain fatty acids controls the Ca(2+) concentration in the cytoplasm. The molecular mechanisms underlying this Ca(2+) mobilization are not fully understood. We show here that the addition of low micromolar concentrations of fatty acids directly to the purified plasma membrane Ca(2+)-ATPase enhance ATP hydrolysis, while higher concentration decrease activity, exerting a dual effect on the enzyme. The effect of arachidonic acid is similar in the presence or absence of calmodulin, acidic phospholipids or ATP at the regulatory site, thereby precluding these sites as probable acid binding sites. At low arachidonic acid concentrations, neither the affinity for calcium nor the phosphoenzyme levels are significantly modified, while at higher concentrations both are decreased. The action of arachidonic acid is isoenzyme specific. The increase on ATP hydrolysis, however, is uncoupled from calcium transport, because arachidonic acid increases the permeability of erythrocyte membranes to calcium. Oleic acid has no effect on membrane permeability while linoleic acid shows an effect similar to that of arachidonic acid. Such effects might contribute to the entry of extracellular Ca(2+) following to fatty acid release.
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Affiliation(s)
- Vanessa H Oliveira
- Instituto de Bioquímica Médica, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha do Fundão, Rio de Janeiro, RJ, Brazil
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Mazzitelli LR, Adamo HP. The phosphatase activity of the plasma membrane Ca2+ pump. Activation by acidic lipids in the absence of Ca2+ increases the apparent affinity for Mg2+. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:1777-83. [PMID: 17540337 DOI: 10.1016/j.bbamem.2007.04.019] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2006] [Revised: 04/20/2007] [Accepted: 04/23/2007] [Indexed: 11/15/2022]
Abstract
The purified PMCA supplemented with phosphatidylcholine was able to hydrolyze pNPP in a reaction media containing only Mg(2+) and K(+). Micromolar concentrations of Ca(2+) inhibited about 75% of the pNPPase activity while the inhibition of the remainder 25% required higher Ca(2+) concentrations. Acidic lipids increased 5-10 fold the pNPPase activity either in the presence or in the absence of Ca(2+). The activation by acidic lipids took place without a significant change in the apparent affinities for pNPP or K(+) but the apparent affinity of the enzyme for Mg(2+) increased about 10 fold. Thus, the stimulation of the pNPPase activity of the PMCA by acidic lipids was maximal at low concentrations of Mg(2+). Although with differing apparent affinities vanadate, phosphate, ATP and ADP were all inhibitors of the pNPPase activity and their effects were not significantly affected by acidic lipids. These results indicate that (a) the phosphatase function of the PMCA is optimal when the enzyme is in its activated Ca(2+) free conformation (E2) and (b) the PMCA can be activated by acidic lipids in the absence of Ca(2+) and the activation improves the interaction of the enzyme with Mg(2+).
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Affiliation(s)
- Luciana R Mazzitelli
- IQUIFIB-Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, 1113 Buenos Aires, Argentina
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Felix CF, Oliveira VH, Moreira OC, Mignaco JA, Barrabin H, Scofano HM. Inhibition of plasma membrane Ca2+-ATPase by heparin is modulated by potassium. Int J Biochem Cell Biol 2006; 39:586-96. [PMID: 17113336 DOI: 10.1016/j.biocel.2006.10.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2006] [Revised: 09/11/2006] [Accepted: 10/11/2006] [Indexed: 10/24/2022]
Abstract
Heparin is related to several protein receptors that control Ca2+ homeostasis. Here, we studied the effects of heparin on the plasma membrane Ca2+-ATPase from erythrocytes. Both ATP hydrolysis and Ca2+ uptake were inhibited by heparin without modification of the steady-state level of phosphoenzyme formed by ATP. Calmodulin did neither modify the inhibition nor the binding of heparin. Inhibition by heparin was counteracted by K+ but not by Li+. This effect was extended to other sulfated polysaccharides with high number of sulfate residues. Hydrolysis of p-nitrophenylphosphate was equally inhibited by heparin. No evidence for enzyme uncoupling was observed: Ca2+ uptake and ATP hydrolysis remained tightly associated at any level of heparin, and heparin did not increase the passive Ca2+ efflux of inside-out vesicles. Vanadate blocked this efflux, indicating that the main point of Ca2+ escape from these vesicles was linked to the Ca2+ pump. It is discussed that sulfated polysaccharides may physiologically increase the steady-state level of Ca2+ in the cytosol by inhibiting the Ca2+ pumps in a K+ (and tissue) regulated way. It is suggested that heparin regulates the plasma membrane Ca2+-ATPase by binding to the E2 conformer.
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Affiliation(s)
- Carla F Felix
- Instituto de Bioquímica Médica, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha do Fundão, Rio de Janeiro, RJ 21941-590, Brazil
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8
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Zhang J, Zhao Y, Duan J, Yang F, Zhang X. Gangliosides activate the phosphatase activity of the erythrocyte plasma membrane Ca2+-ATPase. Arch Biochem Biophys 2005; 444:1-6. [PMID: 16256935 DOI: 10.1016/j.abb.2005.07.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2005] [Revised: 07/12/2005] [Accepted: 07/13/2005] [Indexed: 10/25/2022]
Abstract
The previous studies showed that gangliosides modulated the ATPase activity of the PMCA from porcine brain synaptosomes [Yongfang Zhao, Xiaoxuan Fan, Fuyu Yang, Xujia Zhang, Arch. Biochem. Biophys. 427 (2004) 204-212]. The effects of gangliosides on the hydrolysis of p-nitrophenyl phosphate (pNPP) catalyzed by the erythrocyte plasma membrane Ca(2+)-ATPase, which was characterized as E(2) conformer of the enzyme, were studied. The results showed that pNPPase activity was stimulated up to seven-fold, depending upon the different gangliosides used with GD1b>GM1>GM2>GM3 approximately Asialo-GM1. Under the same conditions, the ATPase activity was also activated, suggesting that gangliosides should modify both E(1) and E(2) conformer of the enzyme. The Ca(2+), which drove the enzyme to E(1) conformation, inhibited the pNPPase activity, but with the similar half-maximal inhibitory concentrations (IC(50)) in the presence and the absence of gangliosides. Moreover, the pNPPase activity was also inhibited by the raise in ATP concentrations. Gangliosides caused a large increase in V(max), but had no effect on the apparent affinity (K(m)) of the enzyme for pNPP. The kinetic analysis indicated that gangliosides could modulate the erythrocyte PMCA through stabilizing E(2) conformer.
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Affiliation(s)
- Jie Zhang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, PR China
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Alves-Ferreira M, da Silva ECC, Ferreira-Pereira A, Scofano HM. Regulatory differences between Ca(2+)-ATPase in plasma membranes from chicken (nucleated) and pig (anucleated) erythrocytes. Comp Biochem Physiol C Toxicol Pharmacol 2002; 131:405-15. [PMID: 11976055 DOI: 10.1016/s1532-0456(02)00023-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Kinetic and regulatory properties of the plasma membrane Ca(2+)-ATPase activity from chicken (nucleated) erythrocytes were studied and compared to those from pig (anucleated) erythrocytes. In the absence of known activators: (1) Ca(2+) affinity for the Ca(2+)-ATPase activity from nucleated erythrocytes was 12-fold higher than that from pig erythrocytes, and thus the enzyme is sensitive to physiological Ca(2+) concentrations; (2) the enzyme from chicken erythrocytes showed two apparent Km values for ATP, as compared to one apparent Km value displayed by pig erythrocytes; (3) Ca(2+)-ATPase inserted in chicken erythrocyte membranes showed a low sensitivity to activation by phosphatidylinositol-4-phosphate; (4) when p-NPP was used as substrate, the activity of chicken erythrocytes was high, similar to that attained by pig erythrocytes, but barely sensitive to activation by dimethylsulfoxide and calmodulin. ATP hydrolysis was 10-fold lower than that displayed by pig erythrocytes and the maximal velocity was activated three-fold by calmodulin. The enzyme was insensitive to alkaline phosphatase treatment and showed a single phosphorylation band in electrophoresis, ruling out the possibility of previous modulation by endogenous kinases and/or by partial proteolysis. The differences may be attributed to some endogenous modulator, to distinct isoforms, or to a difference in the E(1)/E(2) states of the enzyme.
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Affiliation(s)
- Marcelo Alves-Ferreira
- Departamento de Bioquímica Médica, ICB/CCS, UFRJ, CEP 21941-590, Rio de Janeiro, RJ, Brazil
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Freire MM, Mignaco JA, de Carvalho-Alves PC, Barrabin H, Scofano HM. 3-O-methylfluorescein phosphate as a fluorescent substrate for plasma membrane Ca2+-ATPase. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1553:238-48. [PMID: 11997133 DOI: 10.1016/s0005-2728(01)00245-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
3-O-methylfluorescein phosphate hydrolysis, catalyzed by purified erythrocyte Ca2+-ATPase in the absence of Ca2+, was slow in the basal state, activated by phosphatidylserine and controlled proteolysis, but not by calmodulin. p-Nitrophenyl phosphate competitively inhibits hydrolysis in the absence of Ca2+, while ATP inhibits it with a complex kinetics showing a high and a low affinity site for ATP. Labeling with fluorescein isothiocyanate impairs the high affinity binding of ATP, but does not appreciably modify the binding of any of the pseudosubstrates. In the presence of calmodulin, an increase in the Ca2+ concentration produces a bell-shaped curve with a maximum at 50 microM Ca2+. At optimal Ca2+ concentration, hydrolysis of 3-O-methylfluorescein phosphate proceeds in the presence of fluorescein isothiocyanate, is competitively inhibited by p-nitrophenyl phosphate and, in contrast to the result observed in the absence of Ca2+, it is activated by calmodulin. In marked contrast with other pseudosubstrates, hydrolysis of 3-O-methylfluorescein phosphate supports Ca2+ transport. This highly specific activity can be used as a continuous fluorescent marker or as a tool to evaluate partial steps from the reaction cycle of plasma membrane Ca2+-ATPases.
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Affiliation(s)
- Monica M Freire
- Departamento de Bioquímica Médica, Instituto de Ciências Biomédicas, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Cidade Universitária, CEP 21941-590, Rio de Janeiro, Brazil
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McConnell EJ, Wagoner MJ, Keenan CE, Raess BU. Inhibition of calmodulin-stimulated (Ca2+ + Mg2+)-ATPase activity by dimethyl sulfoxide. Biochem Pharmacol 1999; 57:39-44. [PMID: 9920283 DOI: 10.1016/s0006-2952(98)00259-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Membrane-bound (Ca2+ + Mg2+)-ATPase activity from human erythrocyte white ghosts in the calmodulin-activated state was inhibited by DMSO in concentrations of 3% (v/v) and above. At 10%, DMSO inhibited calmodulin activation by 47.7%, while basal, calmodulin-independent (Ca2+ + Mg2+)-ATPase and (Mg2+)-ATPase activity remained unaffected. (Na+ + K+)-ATPase activity was also reduced but exhibited a greater IC50. Concentration-effect analyses showed the inhibition by 10% DMSO to be a reversible, non-competitive effect with regard to calmodulin, Ca2+, and substrate activation. Calmodulin-stimulated processes may be more susceptible to inhibition by DMSO than related enzymatic catalysis, and thus may help explain the multitude of reported cellular events caused by the solvent. Furthermore, DMSO affected membrane-associated enzymatic mechanisms opposite to those reported for purified enzyme outside its native membrane environment.
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Affiliation(s)
- E J McConnell
- Department of Pharmacology and Toxicology, Indiana University School of Medicine, Evansville 47712, USA
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