title: The activation of ox-brain NAD+-dependent isocitrate dehydrogenase by magnesium ions.
abstract: Two independent methods were used to assess the dependence of the activity of ox brain NAD+-dependent isocitrate dehydrogenase on the concentration of magnesium ions. The results indicated the complex between magnesium and isocitrate to be the true substrate for the enzyme. Free isocitrate is neither a substrate nor an inhibitor of the enzyme but free magnesium ions inhibit competitively with respect to the magnesium-isocitrate complex. The inhibition of the enzyme by ATP and citrate appears to be largely explicable in terms of their effects on the concentration of the complex between Mg2+ and isocitrate. The dependence of the activation of the enzyme by ADP on the concentration of magnesium ions suggests that free ADP, rather than its complex with Mg2+, is the activator.
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002417:Cattle; D002951:Citrates / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D066298:In Vitro Techniques; D007521:Isocitrate Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D009243:NAD / Q000494:pharmacology; D013379:Substrate Specificity
chemical_list: D002951:Citrates; D009243:NAD; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D007521:Isocitrate Dehydrogenase; D008274:Magnesium