Regulation of NAD+-linked isocitrate dehydrogenase and 2-oxoglutarate dehydrogenase by Ca2+ ions within toluene-permeabilized rat heart mitochondria. Interactions with regulation by adenine nucleotides and NADH/NAD+ ratios.
1. Toluene-permeabilized rat heart mitochondria have been used to study the regulation of NAD+-linked isocitrate dehydrogenase and 2-oxoglutarate dehydrogenase by Ca2+, adenine and nicotinamide nucleotides, and to compare the properties of the enzymes in situ, with those in mitochondrial extracts. 2. Although K0.5 values (concn. giving half-maximal effect) for Ca2+ of 2-oxoglutarate dehydrogenase were around 1 microM under all conditions, corresponding values for NAD+-linked isocitrate dehydrogenase were in the range 5-43 microM. 3. For both enzymes, K0.5 values for Ca2+ observed in the presence of ATP were 3-10-fold higher than those in the presence of ADP, with values increasing over the ADP/ATP range 0.0-1.0. 4. 2-Oxoglutarate dehydrogenase was less sensitive to inhibition by NADH when assayed in permeabilized mitochondria than in mitochondrial extracts. Similarly, the Km of NAD+-linked isocitrate dehydrogenase for threo-Ds-isocitrate was lower in permeabilized mitochondria than in extracts under all the conditions investigated. 5. It is concluded that in the intact heart Ca2+ activation of NAD+-linked isocitrate dehydrogenase may not necessarily occur in parallel with that of the other mitochondrial Ca2+-sensitive enzymes, 2-oxoglutarate dehydrogenase and the pyruvate dehydrogenase system.
Department of Biochemistry, University of Bristol Medical School, U.K.
G A
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Rutter
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Denton
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D007521:Isocitrate Dehydrogenase / Q000378:metabolism*; D007655:Ketoglutarate Dehydrogenase Complex / Q000378:metabolism*; D007656:Ketoglutaric Acids / Q000378:metabolism; D007658:Ketone Oxidoreductases / Q000378:metabolism*; D007700:Kinetics; D008929:Mitochondria, Heart / Q000187:drug effects / Q000201:enzymology*; D009243:NAD / Q000378:metabolism*; D051381:Rats; D014050:Toluene
D007656:Ketoglutaric Acids; D009243:NAD; D014050:Toluene; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D007521:Isocitrate Dehydrogenase; D007658:Ketone Oxidoreductases; D007655:Ketoglutarate Dehydrogenase Complex; D002118:Calcium