The effects of sterigmatin and its structural isomer, demethylsterigmatocystin, on mitochondrial respiration were studied in comparison with sterigmatocystin. Both compounds uncoupled the oxidative phosphorylation of rat liver mitochondria, causing marked decreases in RC index and P/O ratio. Sterigmatin, in which the xanthone and dihydrobisfuran moieties are fused in a linear style, was more toxic to mitochondrial function than demethylsterigmatocystin which had an angular shape. In addition, the uncoupling activity of sterigmatocystin was markedly decreased by its demethylation.
