title: Electron-transport pathway of the NADH-dependent haem oxygenase system of rat liver microsomal fraction induced by cobalt chloride.
abstract: The hepatic microsomal haem oxygenase activity of rats treated with CoCl2 was studied kinetically by measuring biliverdin, the immediate product of the reaction. Biliverdin was extracted with diethyl ether/ethanol mixture, and was determined by the difference between A690 and A800. The apparent Km value for NADPH (at 50 microM-haematin) was about 0.2 microM when an NADPH-generating system was used, whereas that for NADH was about 630 microM. Essentially the same Vmax. values were obtained for both the NADH- and NADPH-dependent haem oxygenase reactions. No synergism was observed with NADH and NADPH. The NADH-dependent reaction was competitively inhibited by NADP+, with a Ki of about 10 microM. The inhibitoin of the NADH-dependent reaction by the antibody against rat liver microsomal NADPH-cytochrome c reductase was essentially complete, with a pattern similar to that of the NADPH-dependent reaction. The immunochemical experiment and the comparison of the kinetic values with the reported data on isolated NADH-cytochrome b5 reductase and NADPH--cytochrome c reductase indicated the involvement of the latter enzyme in NADH-dependent haem oxygenation by microsomal fraction in situ.
mesh_terms: D000818:Animals; D001664:Biliverdine / Q000096:biosynthesis; D003035:Cobalt / Q000494:pharmacology*; D004579:Electron Transport / Q000187:drug effects; D004790:Enzyme Induction / Q000187:drug effects; D006418:Heme; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism*; D009243:NAD / Q000494:pharmacology; D009249:NADP / Q000494:pharmacology; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D051381:Rats
chemical_list: D009243:NAD; D003035:Cobalt; D006418:Heme; D009249:NADP; D006899:Mixed Function Oxygenases; D009251:NADPH-Ferrihemoprotein Reductase; D001664:Biliverdine