title: [Stoichiometry of microsomal oxidation reactions. Distribution of redox-equivalents in monooxygenase and oxidase reactions catalyzed by cytochrome P-450].
abstract: The stoichiometry of NADPH oxidation in rabbit liver microsomes was studied. It was shown that in uncoupled reactions cytochrome P-450, besides O2- generation catalyzes direct two- and four-electron reduction of O2 to produce H2O2 and water, respectively. With an increase in pH and ionic strength, the amount of O2 reduced via an one-electron route increases at the expense of the two-electron reaction. In parallel, with a rise in pH the steady-state concentration of the oxy-complex of cytochrome P-450 increases, while the synergism of NADPH and NADH action in the H2O2 formation reaction is replaced by competition. The four-electron reduction is markedly accelerated and becomes the main pathway of O2 reduction in the presence of a pseudo-substrate--perfluorohexane. Treatment of rabbit with phenobarbital, which induces the cytochrome P-450 isozyme specific to benzphetamine results in a 2-fold increase in the degree of coupling of NADPH and benzphetamine oxidation. The experimental results suggest that the ratio of reactions of one- and two-electron reduction of O2 is controlled by the ratio of rates of one- and two-electron reduction of cytochrome P-450. In the presence of pseudo-substrates cytochrome P-450 acts predominantly as a four-electron oxidase; one of possible reasons for the uncoupling of microsomal monooxygenase reactions is the multiplicity of cytochrome P-450 isozymes.
mesh_terms: D000815:Aniline Hydroxylase / Q000378:metabolism; D000818:Animals; D001589:Benzphetamine / Q000378:metabolism; D002384:Catalysis; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004579:Electron Transport; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology* / Q000378:metabolism; D008954:Models, Biological; D009249:NADP / Q000378:metabolism*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D011817:Rabbits; D013379:Substrate Specificity
chemical_list: D001589:Benzphetamine; D009249:NADP; D003577:Cytochrome P-450 Enzyme System; D010088:Oxidoreductases; D000815:Aniline Hydroxylase
vernacular_title: Stekhiometriia reaktsii mikrosomal'nogo okisleniia. Raspredelenie redoks-ékvivalentov mezhdu monooksigenaznymi i oksidaznymi reaktsiiami, kataliziruemymi tsitokhromom P-450.