Tricarboxylic acid-cycle activity in mitochondria from Vigna sinensis

Abstract

The activity of enzymes of the tricarboxylic acid cycle in mitochondria from Vigna sinesis (Linn.) Savi has been studies. The oxidation of pyruvated requires a trace amount of some intermediate of the cycle and proceeds even at a tonicity of 0.8 M sucrose. Acetyl-CoA is oxidized rapidly, while acetate or acetyl phosphate is not. Isocitric dehydrogenase is DPN-specific. TPN slightly inhibits DPN-catalyzed oxidation of citrate and cis-aconitate. In the oxidation of α-ketoglutarate, AMP is replaceable by ADP, ATP and partially by CoA. DPN and thianmine pyrophosphate are also stimulatory. Semicarbazide and arsenite inhibit the oxidation completely while hydroxylamine is inert. AMP inhibits oxidation of succinate and this inhibition is accentuated in the presence of CoA or DPN and cannot be reversed by methylene blue or cyanide. Bovine serum albumin and ethanol individually favour oxidatin of succinate, while azide inhibits it. Oxidation of fumarate and l-malate is feeble unless methylene blue and cyanide are added. Oxaloacetate is not oxidized and inhibits the oxidation of some other intermediates of the cycle. The preparation possesses ATPase and adenylate kinase activity. The P/O ratio for succinate at 20° is 1.70.