NAD-specific Isocitrate Dehydrogenase From Bovine Heart. Interaction With Ca2+ Chelators

Biochem J. 1985 Aug 1;229(3):817-22. doi: 10.1042/bj2290817.

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+.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 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

Substances

  • Chelating Agents
  • Citrates
  • Macromolecular Substances
  • NAD
  • Citric Acid
  • NADP
  • Adenosine Diphosphate
  • Isocitrate Dehydrogenase
  • Calcium