Studies on the oxidative half-reaction of xanthine oxidase.

摘要: The oxidative half-reaction of xanthine oxidase is reexamined with regard to the generation superoxide anion. By using cytochrome c reduction monitor superoxide, it found that stoichiometry produced enzyme reoxidized 2:1, significantly greater than previously reported (Olson, J. S., Ballou, D. P., Palmer, G., and Massey, V. (1974) Biol. Chem. 249, 4350-4362). Furthermore, kinetics superoxide-dependent exhibits a pronounced lag during rapid phase reoxidation limiting rate identical slow reoxidation. This indicates generated only in last steps sequential removal reducing equivalents from by molecular oxygen. Experiments two-electron-reduced indicate too produces two ions for each molecule reoxidized, demonstrating electrons leave course form superoxide. scheme must therefore be 6 leads 4 2 1 0, where numbers reflect number intermediate. Using this scheme, both can accurately simulated. Reasons different behavior compared six- four-electron-reduced are discussed.