Interactions of the regulatory ligands Mg2+ and MgATP2- with the renal plasma membrane Ca(2+)-ATPase: effects of osmolytes that stabilize or destabilize protein structure.
In this report we analyze the kinetics of activation of the plasma membrane Ca(2+)-ATPase from kidney proximal tubules by the regulatory ligands Mg2+ and MgATP2-, and we examine modifications in the effects of these ligands that are promoted by organic solutes of natural occurrence that stabilize or destabilize protein structure and function. The solutes tested were trimethylamine-N-oxide (TMA-O), sucrose and urea. TMA-O and sucrose were chosen as representative of the different methylamines and polyols, respectively, that accumulate in living organisms. The results lead to the conclusion that free Mg2+ and the MgATP2- complex both activate the rate-determining E2-->E1 transition during the catalytic cycle of the enzyme, by binding to nonidentical and independent regulatory sites. They also indicate that TMA-O, sucrose and urea not only promote global modifications in the enzyme structure, but also modify specific interactions of the ligands Mg2+ and MgATP2- at their regulatory sites.
Vieyra
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A
Departamento de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Brasil.
Caruso-Neves
C
C
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D000252:Calcium-Transporting ATPases / Q000187:drug effects / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D004347:Drug Interactions; D004789:Enzyme Activation / Q000187:drug effects; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000201:enzymology*; D008024:Ligands; D008274:Magnesium / Q000378:metabolism*; D008744:Methylamines / Q000494:pharmacology; D016877:Oxidants / Q000494:pharmacology; D011817:Rabbits; D013395:Sucrose / Q000494:pharmacology; D014508:Urea / Q000494:pharmacology
D008024:Ligands; D008744:Methylamines; D016877:Oxidants; D013395:Sucrose; D000255:Adenosine Triphosphate; D014508:Urea; D000252:Calcium-Transporting ATPases; C005855:trimethyloxamine; D008274:Magnesium