A new inhibitor of the CoQ-dependent redox reactions in mitochondria and chromatophores

The effects of 3,4-dimethoxyphenyl-1-amylketone (DPK) on the CoQ-dependent stages of the electron transport systems in mitochondria and Rhodobacter sp haeroides chromatophores were studied. The two systems contain the complete Q-cycle. The sensitivities of the Q-cycles of two electron transport syste ms to antimycin, myxothiazole, and other inhibitors are virtually indisting uishable from one another, but these systems have different CoQ reduction p rocesses. The dependence of the inhibition extent of the mitochondrial succ inate oxidase on the DPK concentration was studied. The effective concentra tion of DPK is 0.5-2.5 mM. The presence of the point of inflection in the t itration curve indicates that there are two mechanisms of inhibition. The e ffects of DPK on the extent of reduction of cytochromes b and c(1) + c in m itochondria as well as on the electrogenic stages of the Q-cycle in chromat ophores were examined. The experiments showed that DPK prevents three CoQ-d ependent reactions related to the Q-cycle: electron transport between succi nate dehydrogenase and the Q-cycle in mitochondria and functioning of the Z (o) and C (i) sites of the Q-cycle in chromatophores. DPK does not affect the electrogenic reaction associated with protonation of the secondary quin one acceptor Q(B) in the reaction center of chromatophores. The mitochondri al NADH-dehydrogenase is inhibited by DPK at lower but comparable concentra tions (C-50 = 0.2 mM).