| Abstract: | Intact mitochondria isolated from Jerusalem artichoke tubersoxidize both malate and citrate. Both substrates were equallyeffective in reducing the endogenous pool of pyridine nucleotidesin the presence of respiratory inhibitors. Only malate, andnot citrate, was capable of reducing exogenous NAD+ under similarassay conditions. The rate at which malate reduced added NAD+was biphasic; the initial rapid phase was inhibited by the accumulationof oxaloacetate while the velocity of the second, slower, phasewas found to be insensitive to accumulated oxaloacetate. Theaddition of the detergent Decon 90 to intact mitochondria stimulatedboth the rapid and slow phases of NAD+ reduction and failedto convert the biphasic rate into a constant rate. Decon 90was found to cause inhibition of soluble malate dehydrogenase.Extensive efforts to purify the mitochondria using sucrose densitygradients failed to remove all of the soluble malate dehydrogenasefrom the preparation of mitochondria and approximately 3% ofthe total malate dehyrogenase present in the preparation appearedto behave as if it were outside the inner membrane. |
