Effects of anthraquinone pigments, skyrin and emodin, on mitochondrial reactions have been compared. Both pigments exhibited the uncoupling effects on oxidative phosphorylation of isolated rat liver mitochondria, accompaning a weak inhibition on state 3 respiration. Emodin exhibited much stronger uncoupling effect than that of skyrin. O-methylated derivatives of skyrin and emodin at 6, 6'-and 6-hydroxyl group, respectively, did not uncouple mitochondrial respiration, indicating the involvement of these phenolic hydroxyl groups in the uncoupling actions on the oxidative phosphorylation of mitochondria. Skyrin induced mitochondrial swelling in KCl isotonic solution. Whereas emodin die not induce. These results indicate that biological properties of skyrin, which has dimer structure of emodin, and emodin are of some differences from each oter.
Effect of xanthomegnin on respiratory chain of beef heart mitochondria has been investigated by experiments with electron transport particles and enzymes purified from beef heart mitochondria. It was observed, in the experiment with electron transport particles, that xanthomegnin was reduced by NAD-linked respiratory chain but was not reduced by succinate-linked respiratory chain in aerobic condition. Xanthomegnin was quickly reduced upon addition of NADH and was re-oxidized when NADH was exhausted. Xanthomegnin was reduced by purified NADH dehydrogenase complex in the presence of NADH and electrons were passed to cytochrome c without ubiquinone and cytochrome b·c1 complex. The oxygen consumption was markedly accelerated when cytochrome c was added to a reaction mixture which was composed of NADH dehydrogenase complex, cytochrome oxidase, xanthomegnin, and NADH. These results demonstrate that xanthomegnin produces an electron transport shunt from NADH dehydrogenase to cytochrome c in the respiratory chain of mitochondria.