The in Vitro Effects of Tannic Acid on Rat Liver Mitochondrial Respiration and Oxidative Phosphorylation(Biological)

  • 足立 博一
    Department of Hospital Pharmacy, Toyama Medical and Pharmaceutical University
  • 古西 清司
    Department of Biochemistry, Faculty of Medicine, Toyama Medical and Pharmaceutical University
  • 鳥居塚 一夫
    Department of Sino-Japanese (Kampoh) Medicine, Toyama Medical and Pharmaceutical University
  • 堀越 勇
    Department of Hospital Pharmacy, Toyama Medical and Pharmaceutical University

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The in vitro effects of tannic acid on the membrane structure and function of rat liver mitochondria were investigated. The respiratory control ratio (RCR) decreased by about 50% on addition of 50μg/ml tannic acid to highly coupled mitochondria, but the adenosine-5'-diphosphate/oxygen (ADP/O) ratio was constant. The uncoupler-induced respiration was also inhibited in the same manner as the RCR. Moreover, the respiratory control disappeared and the ADP/O ratio could not be measured at concentrations of tannic acid above 100μg/ml. On the other hand, the oxygen consumption rate of succinate-dependent respiration decreased on addition of more than 100/fg/ml tannic acid (50% inhibitory concentration (IC_<50>)=150μg/ml tannic acid) to mitochondria. These findings suggest that tannic acid at lower concentrations inhibits the electron transport system to decrease the RCR, but does not impair the membrane, retaining the coupled reaction, while at higher concentrations it impairs the structural integrity of mitochondrial membranes, and directly inhibits the electron transport system. Tannic acid inhibited the succinate oxidase, reduced njcotinamide adenine dinucleotide (NADH) oxidase, succinate dehydrogenase, and NADH dehydrogenase activities of submito-chondrial particles (SMP). The IC_<50> values of tannic acid toward these enzyme systems were estimated to be 35, 45, 30, and 15μg/ml, respectively. Tannic acid competitively inhibited succinate dehydrogenase and NADH dehydrogenase. However, it did not show significant inhibition of the cytochjrome oxidase activity of SMP. It is thus concluded that tannic acid exerts its effect on rnitochondrial respiration and oxidativc phosphorylation through action on the membrane and on both succinate dehydrogenase and NADH dehydrogenase of mitochondria.

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