Reduced nicotinamide adenine dinucleotide and reduced nicotinamide adenine dinucleotide phosphate diaphorase activity...

Total reduced nicotinamide adenine dinucleotide (NADH) and reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase activities were examined in human neutrophils. Approximately two-thirds of each enzyme activity was located in the granule fraction with the remainder in the soluble. The activities in a 27,000 x g supernatant from a sonic extract of human polymorphonuclear leukocytes were characterized. Both NADH and NADPH diaphorase were insensitive to cyanide and azide and showed greater activity at acid pH. K(m) values for nitroblue tetrazolium were not markedly different (33 muM with NADH and 12 muM with NADPH), but there was a 40-fold difference in K(m) for the reduced pyridine nucleotides (10 muM with NADH and 400 muM for NADPH). Since the intracellular concentration of both nucleotides is estimated to be about 50 muM, it is much more likely, from a kinetic argument, that the respiratory burst of phagocytosis is intiated by the oxidation of NADH rather than of NADPH.