[The effect of isomeric alkyl (C19--C25) methoxybenzoquinones on mitochondrial respiration].

The influence of 2-methoxy-6-alkyl(C19-C25)benzoquinones-1,4 and 4-methoxy-6-alkyl(C19-C25)benzoquinones-1,2 on the respiration of isolated rat liver mitochondria has been studied. As a concentration of each of the quinones increased gradually from zero, the rate of the respiration using NAD-dependent substrates firstly increased but then decreased, 1,2-quinones being the more potent inhibitors. Concurrently, the respiratory control of mitochondria was lowered, indicating uncoupling effect of these quinones. With succinate the latter exhibited moderately accelerating effect. Uncoupled by 2,4-dinitrophenol, the respiration was stimulated by the both preparations in the presence of succinate but was suppressed when NAD-dependent substrates were used. The observed inhibitory effects have been assumed to be caused by a competition between the quinones and endogenous co-enzyme Q for the active site of NADH-dehydrogenase complex of the respiratory chain.