Detection of NADPH diaphorase activity associated with human neutrophil NADPH-O2 oxidoreductase activity

At approximately equimolar concentrations (approximately 70 microM), and in the presence of excess catalase and superoxide dismutase, DCIP, ferricytochrome c and ferricyanide abstracted 21, 6 and 61%, respectively, of the electron equivalents given up by NADPH to the NADPH-O2 oxidoreductase complex derived from phorbol myristate acetate-stimulated human neutrophils. With a 10-fold increase in ferricyanide, all of the electron equivalents given up by NADPH to the oxidoreductase complex were shunted to ferricyanide concomitant with complete inhibition of NADPH-dependent O2 consumption. These results substantiate the existence of intrinsic diaphorase activity associated with the superoxide generating NADPH-O2 oxidoreductase of human neutrophils.