Mechanism of the superoxide-producing oxidase of neutrophils. O2 is necessary for the fast reduction of cytochrome b-245 by NADPH.
A soluble oxidase from phorbol-stimulated pig neutrophils contained FAD and cytochrome b-245. A typical preparation produced 13.03 mol of superoxide (O2-.) X S-1 X mol of cytochrome b-1 (348 nmol X min-1 X mg of protein-1). In the aerobic steady state, cytochrome b was 8.9% reduced. Steady-state cytochrome b reduction was absent from extracts of unstimulated cells; Km values for NADPH, for O2-. production and cytochrome b reduction were similar. The calculated aerobic rate of cytochrome b reduction was equal to the measured rate of O2-. production in a variety of preparations and in the presence of a range of inhibitors. Under anaerobic conditions the rate was slow: O2 is apparently required for rapid electron flow into the oxidase complex. Cytochrome b is shown to be kinetically competent to act as part of the O2-.-generating complex.
Cross
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Parkinson
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JF
Jones
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OT
D000818:Animals; D003573:Cytochrome b Group / Q000378:metabolism*; D004227:Dithionite / Q000494:pharmacology; D007700:Kinetics; D009247:NADH, NADPH Oxidoreductases / Q000037:antagonists & inhibitors / Q000097:blood*; D009249:NADP / Q000378:metabolism*; D019255:NADPH Oxidases; D009504:Neutrophils / Q000201:enzymology*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D013053:Spectrophotometry; D013481:Superoxides / Q000378:metabolism; D013552:Swine
D003573:Cytochrome b Group; C035130:cytochrome b245; D013481:Superoxides; D004227:Dithionite; D009249:NADP; D009247:NADH, NADPH Oxidoreductases; D019255:NADPH Oxidases; C022709:superoxide-forming enzyme; D010100:Oxygen