title: On the mechanism of one-electron reduction of quinones by microsomal flavin enzymes: the kinetic analysis between cytochrome B5 and menadione.
abstract: Univalent oxidation-reduction reactions coupled with the menadione (MK)/menadione semiquinone (MK.-) system were investigated by using microsomal flavin enzymes. NADPH-cytochrome P-450 reductase gave a dynamic equilibrium of oxidation-reduction of cytochrome b5 in the presence of menadione (MK), the level of which depended on the concentration of O2 and superoxide dismutase. The data suggest that the superoxide and menadione radicals are involved as an active intermediate in this system. The overall reaction at steady state appears to be composed of four main reactions, eqs. 2-5, and eqs. 2 and 4 are in equilibrium.
authors.affiliation: Institute of Basic Medical Sciences, University of Tsukuba, Ibaraki, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Iyanagi
mesh_terms: D000818:Animals; D015786:Cytochromes b5 / Q000378:metabolism*; D004583:Electrons; D066298:In Vitro Techniques; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000187:drug effects; D011809:Quinones / Q000032:analysis*; D013482:Superoxide Dismutase / Q000494:pharmacology; D013552:Swine; D014812:Vitamin K / Q000378:metabolism*
chemical_list: D011809:Quinones; D014812:Vitamin K; D015786:Cytochromes b5; D013482:Superoxide Dismutase; D009251:NADPH-Ferrihemoprotein Reductase