Abstract
The succinic oxidase system of heart-muscle and kidney prepns. was inactivated by treatment with a number of reducing agents in the presence of air. Under certain conditions, many of these reducing agents had little effect on the succinic dehydrogenase. BAL had 2 quite distinct effects: (a) complete inactivation of the succinic oxidase system, without any effect on the succinic dehydrogenase; (b) a partial inhibition of succinic dehydrogenase, which did not occur until more than half the BAL had been oxidized. The latter inhibition was probably due to oxidation of SH groups. The former inhibition was studied in detail. Oxidized BAL inhibited the succinic oxidase system much less than BAL, while no inhibition occurred if the enzyme prepn. was treated with BAL under anaerobic conditions. H2O2 was produced during the oxidation of BAL in buffer soln. or in the presence of heart-muscle prepn. Some substance (or substances) was oxidized during treatment of heart-muscle prepn. with BAL in the presence of air. H2O2 produced by notatin-glucose and by D-amino acid oxidase and its substrates had a much less pronounced effect on the succinic oxidase system than BAL. Inhibition by these substances was increased by catalase and decreased by ethanol and pyruvate. Catalase, ethanol and pyruvate had no effect on the inhibition of the system caused by BAL. The addition of Cu, which increased the rate of oxidation of BAL, decreased the inactivation of the succinic oxidase system, but increased that of succinic dehydrogenase. It was concluded that the inhibition produced by BAL was not due to the H2O2 formed during the oxidation of BAL, but was caused by the directly coupled oxidation of BAL, not involving free H2O2, with some substance or grouping necessary for the activity of the succinic oxidase system. The presence of cytochrome c, during the treatment of the enzyme with the BAL, prevented the inactivation of the enzyme. Treatment with BAL did not affect the true cytochrome oxidase activity. Treatment with BAL did not destroy the cytochromes; a protohematin compound, amounting to about 20% of the total protohematin content of the heart-muscle prepn., was, however, destroyed by this treatment. There was some correlation between the amt. of hematin compound destroyed and the degree of inactivation of the succinic oxidase system when different concns. of BAL were allowed to act on the enzyme for various times. Treatment with BAL caused an impairment of the oxidation of cytochrome b by cytochrome c. The cytochrome b was, however, oxidized by methylene blue or dichlorophenolindo-phenol. Evidence was presented in favor of the view that BAL affected the succinic oxidase system by destroying a component of the succinic oxidase system required for the transmission of electrons between cytochrome b and cytochrome c. The component of the succinic oxidase system, which was destroyed by the treatment with the BAL, was probably the same as the hematin compound destroyed by the same treatment.
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