Biochemical studies of pigments from a pathogenic fungus Microsporum cookei IV. Enzymatic reduction of xanthomegnin by mitochondria and microsomes

The enzymatic oxido-reduction of xanthomegnin has been investigated spectroscopically using rat liver mitochondria and microsomes. Xanthomegnin, a binaphthoquinone pigment isolated from a dermatophyte Microsporum cookei, has been shown to strongly uncouple mitochondrial respiration and has been suggested to exert a cyto-toxic effect in animals. The redox response of this pigment has also been suggested to participate in uncoupling of oxidative phosphorylation in mitochondria, by forming a bypass to the electron transport system. In the presence of succinate or L-glutamate as substrate, xanthomegnin was reduced by mitochondria after dissolved oxygen was completely consumed. This suggests that complex IV of the respiratory chain of mitochondria is concerned with enzymatic reduction of xanthomegnin and that its redox response is not involved in the uncoupling effect on mitochondrial respiration. On the other hand, when NADH was added, xanthomegnin was immediately reduced by mitochondria, submitochondrial particles, and microsomes, indicating the xanthomegnin is reduced by NAD-linked electron transport system of mitochondria and microsomes. Xanthomegnin reduced by ascorbate was auto-oxidized by dissolved oxygen.These results would indicate that xanthomegnin forms an electron transport bypass to the NAD-linked respiratory chain and readily oxidize cytosol NADH. This may cause the cyto-toxic effect to animals.