The reaction of reduced xanthine oxidase with oxygen. Kinetics of peroxide and superoxide formation.

摘要: Product formation during the oxidation of xanthine oxidase has been examined directly by using cytochrome c peroxidase as a trapping agent for hydrogen peroxide and reduction measure superoxide formation. When fully reduced enzyme is mixed with high concentrations oxygen, 2 molecules H2O2/flavin are produced rapidly, while 1 molecule O2-/flavin rapidly another much more slowly. Time courses those absorbance changes due to were fitted successfully mechanism proposed earlier (Olson, J. S., Ballou, D. P., Palmer, G., Massey, V. (1974) Biol. Chem. 249, 4363-4382). In this scheme, each oxidative step initiated very rapid reversible an oxygen.FADH2 complex (the apparent KD = 2.2 X 10(-4) M at 20 degrees C, pH 8.3). cases 6- 4-electron-reduced enzyme, electrons transferred (ke 60 s-1) generate partially oxidized oxidase. case 2-electron-reduced only electron produced. The remaining remains in iron-sulfur centers removed slowly second order process (ks 10(4) M-1 s-1). decreased from 9.9 6.2, both oxygen binding rate transfer about 20-fold. This result suggestive uncompetitive inhibition implies that proton enzyme-flavin active site affects primarily transfer, not initial complex.