Abstract
The effects of versicolorins A & B on the respiratory chains of mitochondria were studied using electron transport particles (ETP) prepared from rat liver mitochondria. Both compounds depressed the respiration of ETP, exerting markedly stronger inhibition on NAD-linked than on succinate-linked respiratory system. Of the two compounds, versicolorin B, which has bis-tetrahydrofuran ring, was found to be eminently stronger inhibitor than versicolorin A which had bis-dihydrofuran ring. Neither succinate dehydro-genase (complex II) nor cytochrome c oxidase (complex IV) of the respiratory chain was affected by both compounds. NADH-CoQ2 reductase (complex I) and durohydroquinone oxidase (complex III and IV) activities were depressed by these compounds, exerting a stronger inhibition on the latter reaction. These results apparently indicate that versico-lorins A & B interefere mainly with the redox reaction of the complex III (cytochrome bci complex) and at the same time weakly with complex I (NADH-CoQ10 reductase). It was thus concluded that versicolorins A & B depressed mitochondrial respiration by direct interactions with respiratory enzymes involving in the electron transport system in mito-chondria.
