title: Inhibitory effects of tannins on the NADH dehydrogenase activity of bovine heart mitochondrial complex I.
abstract: NADH-quinone oxidoreductase is classified into two groups, NADH dehydrogenase-1 (NDH-1) and NADH dehydrogenase-2 (NDH-2). Animal mitochondrial complex I is an NDH-1 type enzyme. Previously, we isolated potent inhibitors from plants to both NDH-1 and NDH-2. We have now examined detailed inhibitory effects of three tannins (pentagalloylglucose, sanguiin H-11, and oolonghomobisflavan A) on NDH-1 using bovine heart mitochondrial complex I and a subcomplex flavoprotein (containing 3 subunits) derived from complex I. Although many specific inhibitors of NDH-1 (e.g. rotenone and piericidin A) have been reported, the reactive sites are at or near to, the ubiquinone-binding site. NADH-ubiquinone-1 oxidoreductase activity of complex I was inhibited by the three tannins, among which sanguiin H-11 was the most potent inhibitor. NADH-menadione oxidoreductase activity of complex I was susceptible to the three tannins, but completely resistant to rotenone. The inhibitory effects of tannins were all noncompetitive with respect to NADH, ubiquinone-1, and menadione. The NADH-menadione oxidoreductase of flavoprotein was also inhibited by the three tannins, but not by rotenone, which is consistent with the fact that flavoprotein does not contain a native ubiquinone-binding site. The study of the NADH reduced-minus-oxidized difference spectrum of flavoprotein under steady-state conditions indicated that the inhibitory sites of sanguiin H-11 and oolonghomobisflavan A exist between the NADH binding site and the FMN site, and that for pentagalloylglucose exists between FMN and an artificial electron acceptor-binding site. These results suggest that the tannins are potent inhibitors of NADH dehydrogenases, and that the inhibitory mechanisms are novel.
authors.affiliation: Department of Microbiology, Nippon Dental University School of Dentistry at Tokyo, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Konishi
authors.forename: T
authors.initials: T
authors.lastname: Tanaka
mesh_terms: D000818:Animals; D002417:Cattle; D004579:Electron Transport; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D016014:Linear Models; D008929:Mitochondria, Heart / Q000187:drug effects* / Q000201:enzymology; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000037:antagonists & inhibitors*; D009245:NADH Dehydrogenase / Q000037:antagonists & inhibitors*; D013634:Tannins / Q000494:pharmacology*
chemical_list: D004791:Enzyme Inhibitors; D013634:Tannins; D016660:NAD(P)H Dehydrogenase (Quinone); D009245:NADH Dehydrogenase