NAD-specific isocitrate dehydrogenase from bovine heart. Interaction with Ca2+ chelators

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-oxapropa...

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Bibliographic Details
Published in:Biochemical journal 1985-08, Vol.229 (3), p.817-822
Main Authors: Gabriel, J L, Plaut, G W
Format: Article
Language:English
Subjects:
Adenosine Diphosphate - pharmacology
Animals
Calcium - metabolism
Cattle
Chelating Agents - pharmacology
Citrates - pharmacology
Citric Acid
Enzyme Activation - drug effects
Isocitrate Dehydrogenase - antagonists & inhibitors
Kinetics
Macromolecular Substances
Myocardium - enzymology
NAD - pharmacology
NADP - pharmacology
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Summary: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+.
ISSN:0264-6021
1470-8728
DOI:10.1042/bj2290817