COENZYME Q: REVERSAL OF INHIBITION OF SUCCINATE CYTOCHROME C REDUCTASE BY LIPOPHILIC COMPOUNDS.

The activity of a particulate succinate cytochrome c reductase is inhibited by antimycin, 2-heptyl-4-hydroxyquinoline-N-oxide, 2-(9-cyclohexyl-n-nonyl)-3-hydroxy-1,4naphthoquinone and thenoyltrifluoroacetone. The ratio of antimycin A (required for complete inhibition) to the molar content of the cytochrome b of the reductase is approximately 0.5 in contrast to the reported value of 1.0 or higher for succinate oxidase preparations. However, the degreeof inhibition by antimycin is dependent on the exogenous coenzyme Q (ubiquinone) present. Indeed, the inhibition from any of these compounds is competitively reversed by exogenous coenzyme Q in the system.