Inhibition of dihydrocozymase-oxidase activity of heart-muscle preparations of certain cell-free bacterial preparations by 2-heptyl-4-hydroxyquinoline N-oxide

Abstract

The cytochromes of preparations of Staphylococcus aureus, Escherichia coli, Proteus vulgaris and Bacillus pumilus were reduced by added dihydrocozymase (0.66 mM). Oxidation of 0.66 mM-dihydrocozymase by the bacterial preparations was inhibited by heptyl N oxide (4[mu] M). In the presence of 4[mu] M heptyl N oxide with dihydrocozymase (0.33 mM) as substrate, the oxidation of reduced cytochrome b1 of S. aureus preparations was inhibited, but in preparations of E. coli, the reduction of oxidized cytochrome b1 was inhibited. The diaphorase activity of heart muscle preparations and of the cell-free bacterial preparations was not inhibited by heptyl N oxide. Anaerobically, the cytochrome b of the heart muscle preparations was slowly and incompletely reduced by 0.33 mM dihydrocozymase, but complete reduction occurred when the dihydrocozymase was 0.66 mM. Under aerobic conditions when heptyl N oxide or antimycin A was present, strong reduction of cytochrome b of heart muscle preparations was observed, even with low concentrations of dihydrocozymase (0.33 mM). It is suggested that cytochrome b is on the main pathway for electron transport in the dihydrocozymase-oxidase system of the heart muscle preparation. The site of action of heptyl N oxide in the dihydrocozymase-oxidase system of heart muscle is between diaphorase and cytochrome c, and most probably between cytochrome b and cytochrome c. Both heptyl N oxide and antimycin A inhibit "auto-oxidation" of cytochrome b. The significance of this phenomenon is discussed.