Interaction of non-specific reducing and oxidizing agents with the cytochrome system in heart-muscle preparations

Abstract

1. 1. Under anaerobic conditions, 2:3-dimercaptopropanol (BAL), ascorbate and a number of monothiols brought about the reduction of cytochromes b, c and a in Keilin and Hartree heart-muscle preparations. The reduction of cytochrome b under these conditions was relatively slow and incomplete, but was made still slower by the addition of antimycin. 2. 2. Under anaerobic conditions, oxidation of reduced cytochromes b, c and a was brought about by hydrogen peroxide in the presence of cyanide, by o-iodosobenzoate and the disulphide cystamine. The oxidation of cytochrome b under these conditions was relatively fast, but was inhibited by the addition of antimycin. 3. 3. From these experiments it was concluded that antimycin inhibits the respiratory chain between cytochrome b and the point of interaction of these reducing and oxidizing agents, tentatively identified as the BAL-sensitive factor. 4. 4. Succinate, but not malonate, protected the succinic oxidase system from inhibition by BAL in the presence of air. Antimycin, but not cyanide, prevented succinate from protecting the BAL-sensitive factor. 5. 5. From these protection experiments it was concluded that the antimycin-sensitive factor lies between succinic dehydrogenase and the BAL-sensitive factor. 6. 6. Under the conditions of the BAL-air inhibition process, the protective effect of succinate was probably to prevent the oxidation of BAL by making the reaction medium essentially anaerobic. When, however, the oxidation of succinate was limited by addition of cyanide, under these conditions, it was found that oxidation of BAL took place to the extent of about one third of that in the presence of cyanide alone. This amount of oxidation of BAL would be expected to lead to substantial inhibition of succinic oxidase activity, but in fact no inhibition was observed.