[One- and two-electron reduction of ubiquinone homologs by NADH- dehydrogenase preparations from the mitochondrial respiratory chain].

The mechanism of ubiquinone homologs reduction by different preparations of mitochondrial NADH dehydrogenase: complex I within submitochondrial particles, isolated NADH-ubiquinone oxidoreductase and soluble low molecular weight NADH dehydrogenase, has been investigated. It has been shown that NADH oxidation via the rotenone-insensitive reaction is associated with one-electron reduction of low molecular weight ubiquinone homologs (Q0, Q1, Q2) to semiquinone with subsequent fast oxidation of the latter by atmospheric oxygen to form a superoxide radical. The two-electron ubiquinone reduction to quinol in the rotenone-sensitive reaction is unaccompanied by the semiquinone release from the enzyme active center into the surrounding solution.

[Activation of succinate oxidase in the inner membrane of rat liver mitochondria].

It is shown that the process of activation of succinate oxidase from inner membranes of the rat liver mitochondria by succinate and malonate is specific for the succinate dehydrogenase component of oxidase. These activation constants are comparable with those found by other authors in activation of succinate dehydrogenase and succinate oxidase from oxaloacetate-preincubated submitochondrial fragments of the bull heart. Probably, the 4-fold activation of succinate oxidase from inner membranes of the liver mitochondria reported in this paper depends on separation of endogenous oxaloacetate from the succinate dehydrogenase component of oxidase.

[A method of determining 2-oxoglutarate dehydrogenase activity in intact mitochondria].

A rather simple method is suggested for measuring the activity of 2-oxoglutarate dehydrogenase of intact mitochondria. The method is based on the determination of the rate of exogenic 2-oxoglutarate decrease in the mitochondrial suspension. Experiments with sodium arsenite and comparison of kinetic parameters of the 2-oxoglutarate, dehydrogenase reaction and transport of 2-oxoglutarate to mitochondria have shown that the measurable exogenic 2-oxoglutarate oxidation rate corresponds to the 2-oxoglutarate dehydrogenase activity in intact mitochondria.