Inhibition of mitochondrial NADH oxidase, succinoxidase, and ATPase by naturally occurring flavonoids.

A structure-activity investigation of the inhibition of beef heart mitochondrial NADH oxidase and succinoxidase and rat liver mitochondrial ATPase by flavonoids was conducted. NADH oxidase was the most sensitive to inhibition by flavonoids: 13 of the 18 flavonoids tested inhibited NADH oxidase, whereas only 4 and 5 flavonoids inhibited succinoxidase and ATPase, respectively. The flavonoids possessing a catechol or pyrogallol moiety, and a 2,3-double bond and a 3-hydroxyl group were the most inhibitory towards the respiratory chain enzymes. The catechol or pyrogallol moiety did not exert preferential activity towards the oligomycin-sensitive ATPase because morin, which contains a meta-dihydroxy configuration, was the most potent ATPase inhibitor.