The effects of 1,2,3,4,6-penta-O-galloyl-beta-D-glucose on rat liver mitochondrial respiration

The inhibitory effects of pure galloylglucose (1,2,3,4,6-penta-O-galloyl-beta-D-glucose) on the respiratory chain of rat liver mitochondria were investigated. The respiratory control ratio (RCR) decreased by 50% on addition of 20 microM pentagalloylglucose to highly coupled mitochondria, but the adenosine-5'-diphosphate/oxygen (ADP/O) ratio decreased only slightly. The RCR disappeared and the ADP/O ratio could not be measured at concentrations of pentagalloylglucose above 30 microM. On the other hand, the uncoupler-induced oxygen consumption was also inhibited. These findings suggest that pentagalloylglucose at low concentrations inhibits the electron transport system to decrease the RCR, but scarcely impairs the membrane, practically retaining the coupled reaction, while at high concentrations it impairs the structural integrity of the mitochondrial membrane. Pentagalloylglucose competitively inhibited succinate dehydrogenase activity, and noncompetitively inhibited reduced nicotinamide adenine dinucleotide (NADH) dehydrogenase and ubiquinol-1 oxidase activities of submitochondrial particles (SMP). However, it did not show significant inhibition of the cytochrome c oxidase activity of SMP. It is thus concluded that pentagalloylglucose, which is the lowest-molecular-weight component of tannic acid, exerts its effect on mitochondrial respiration and oxidative phosphorylation through action on the membrane and on succinate dehydrogenase, NADH dehydrogenase and cytochrome bc1 complex of mitochondria.