The reactivity of chicken liver xanthine dehydrogenase with molecular oxygen.

摘要: Abstract The reaction of 6-electron reduced chicken liver xanthine dehydrogenase (XDH) with molecular oxygen was studied using both stopped flow and steady-state turnover techniques at pH 7.8, 4 degrees C. Oxidation fully XDH proceeded via four phases, three which were detected the spectrophotometer. fastest phase second order in (1900 M-1 s-1), resulted appearance flavin semiquinone yielded no superoxide. next also (260 involved loss yielded, on average, 1 mol superoxide/mol oxidized. last 2 electron equivalents located iron-sulfur centers. They released one equivalent a time form Steady-state kinetics found to be critically dependent temperature concentration. When these factors carefully controlled, xanthine-oxygen NADH-oxygen reductase reactions gave linear Lineweaver-Burk plots. data number 43 min-1, 42% that for xanthine-NAD turnover. During turnover, O2, 40-44% introduced by appeared as Reduced pyridine nucleotides, NAD 3-aminopyridine adenine dinucleotide, dramatically formation superoxide levels did not seriously inhibit reactivity.