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 Ravin enzymes. NADPH-cytochrome P-450 reduc-tase gave a dynamic equilibrium of oxidation-reduction of cytochrome b, 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

Key Words:

• One-electron reduction
• menadione
• superoxide
• NADPH-cytochrome P-450 reductase
• cytochrome b₅
• redox cycling.