A kinetic study of the alpha-keto acid dehydrogenase complexes from pig heart mitochondria.
The kinetic mechanisms of the 2-oxoglutarate and pyruvate dehydrogenease complexes from pig heart mitochondria were studied at pH 7.5 and 25 degrees. A three-site ping-pong mechanism for the actin of both complexes was proposed on the basis of the parallel lines obtained when 1/v was plotted against 2-oxoglutarate or pyruvate concentration for various levels of CoA and a level of NAD+ near its Michaelis constant value. Rate equations were derived from the proposed mechanism. Michaelis constants for the reactants of the 2-oxoglutarate dehydrogenase complex reaction are: 2-oxoglutarate, 0.220 mM; CoA, 0.025 mM; NAD+, 0.050 mM. Those of the pyruvate dehydrogenase complex are: pyruvate, 0.015 mM; CoA, 0.021 mM; NAD+, 0.079 mM. Product inhibition studies showed that succinyl-CoA or acetyl-CoA was competitive with respect to CoA, and NADH was competitive with respect to NAD+ in both overall reactions, and that succinyl-CoA or acetyl-CoA and NADH were uncompetitive with respect to 2-oxoglutarate or pyruvate, respectively. However, noncompetitive (rather than uncompetitive) inhibition patterns were observed for succinyl-CoA or acetyl-CoA versus NAD+ and for NADH versus CoA. These results are consistent with the proposed mechanisms.
D000105:Acetyl Coenzyme A / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D003065:Coenzyme A / Q000494:pharmacology; D008058:Dihydrolipoamide Dehydrogenase / Q000378:metabolism; D007655:Ketoglutarate Dehydrogenase Complex / Q000378:metabolism*; D007656:Ketoglutaric Acids / Q000378:metabolism; D007658:Ketone Oxidoreductases / Q000378:metabolism*; D007700:Kinetics; D008931:Mitochondria, Muscle / Q000201:enzymology*; D009206:Myocardium / Q000201:enzymology*; D009243:NAD / Q000494:pharmacology; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism*; D011773:Pyruvates / Q000378:metabolism; D013386:Succinates / Q000494:pharmacology; D013552:Swine
D007656:Ketoglutaric Acids; D011768:Pyruvate Dehydrogenase Complex; D011773:Pyruvates; D013386:Succinates; D009243:NAD; D000105:Acetyl Coenzyme A; D007658:Ketone Oxidoreductases; D007655:Ketoglutarate Dehydrogenase Complex; D008058:Dihydrolipoamide Dehydrogenase; D003065:Coenzyme A