title: NAD-specific isocitrate dehydrogenase from bovine heart. Interaction with Ca2+ chelators.
abstract: The activity of NAD-specific isocitrate dehydrogenase was inhibited by EDTA, EGTA and other nitrogen-containing polycarboxylate Ca2+ chelators in the absence and in the presence of ADP by a mechanism that could not be attributed solely to the removal of free Ca2+. Carboxymethyltartronate (2-oxapropane-1,1,3-tricarboxylate), an oxygen ether polycarboxylate chelator, did not inhibit when ADP was absent. The activation by ADP, a positive effector of the enzyme, decreased with increasing concentration of carboxymethyltartronate, paralleling the removal of free Ca2+ by this chelator. The following were found when free Ca2+ was decreased to negligible concentrations (5-50 nM) with carboxymethyltartronate. (1) Free Ca2+ enhanced, but was not absolutely required for, activation by ADP. (2) Activation of enzyme activity by magnesium citrate neither required nor was increased by Ca2+ when ADP was absent. However, the potentiation of citrate activation by ADP was facilitated by free Ca2+. (3) The reversal of NADPH inhibition of enzyme activity by ADP did not absolutely require Ca2+, but it was enhanced by free Ca2+. (4) The inhibition of enzyme activity by NADH was not reversed by ADP either with or without Ca2+.
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D002614:Chelating Agents / Q000494:pharmacology*; D002951:Citrates / Q000494:pharmacology; D019343:Citric Acid; D004789:Enzyme Activation / Q000187:drug effects; D007521:Isocitrate Dehydrogenase / Q000037:antagonists & inhibitors*; D007700:Kinetics; D046911:Macromolecular Substances; D009206:Myocardium / Q000201:enzymology*; D009243:NAD / Q000494:pharmacology; D009249:NADP / Q000494:pharmacology
chemical_list: D002614:Chelating Agents; D002951:Citrates; D046911:Macromolecular Substances; D009243:NAD; D019343:Citric Acid; D009249:NADP; D000244:Adenosine Diphosphate; D007521:Isocitrate Dehydrogenase; D002118:Calcium