title: Electron spin resonance studies on a flavoprotein in neutrophil plasma membranes. Redox potentials of the flavin and its participation in NADPH oxidase.
abstract: Plasma membrane fractions of stimulated and resting cells were isolated from pig blood neutrophils. The midpoint redox potential (Em) of the membrane-bound flavin was determined potentiometrically by analysis of the flavin free-radical signal by electron spin resonance (ESR) spectroscopy. In both stimulated and resting cells, a peak position of the titration curve gave an Em value of -280 mV at pH 7.0 (Em7). The flavin free radical showed an ESR spectrum at g = 2.004 with a peak to peak width of 19 G, which indicates that the redox intermediate is a neutral semiquinone. Redox titrations were anaerobically examined at 25 degrees C with NADPH in place of dithionite. Addition of NADPH to plasma membranes of stimulated cells resulted in a rapid change in potential, accompanied by the formation of the ESR signal of flavin free radical. Computer simulation of the titration points gave an ambient midpoint potential of -280 mV (Em7). In contrast, those of resting cells showed a very slow change in potential and no g = 2.00 signal formation. Power saturation behavior of the ESR signal showed a marked difference between those of stimulated and resting cells. ESR characteristics of the flavin are discussed in relation to the membrane-bound NADPH oxidase.
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D005420:Flavoproteins / Q000097:blood*; D005609:Free Radicals; D006863:Hydrogen-Ion Concentration; D009247:NADH, NADPH Oxidoreductases / Q000097:blood*; D009249:NADP / Q000494:pharmacology; D019255:NADPH Oxidases; D009504:Neutrophils / Q000378:metabolism*; D010084:Oxidation-Reduction; D011199:Potentiometry; D013552:Swine; D013816:Thermodynamics
chemical_list: D005420:Flavoproteins; D005609:Free Radicals; D009249:NADP; D009247:NADH, NADPH Oxidoreductases; D019255:NADPH Oxidases