Proton stoichiometry associated with human neutrophil respiratory-burst reactions

Control of the intraphagosomal pH in neutrophils may be of importance in creating a microbicidal environment by regulating the activity of the O2-.-generating NADPH oxidase and the lysosomal enzymes discharged into this compartment. In this study, we examined the proton stoichiometry associated with the primary enzymatic reaction underlying the respiratory burst. A preparation of the neutrophil-derived, membrane oxidase consumed NADPH and generated O2-. with a stoichiometry of 1 NADPH:2 O2-. When the enzymatically produced O2-. was prevented from undergoing dismutation, net protons were released in an approximate 1:2 stoichiometry with O2-. generated. In contrast, when O2-. was allowed to dismutate to H2O2, net protons were consumed in a 1:1 stoichiometry with the accumulated H2O2. Thus, the delta pH associated with the NADPH oxidase-dependent production of O2-. was dictated by the fate of the generated radical. The consumption of the oxidase-generated H2O2 by the lysosomal enzyme myeloperoxidase resulted in the formation of HOCl which was trapped in the presence of taurine as the N-chloro derivative. The ratio of chlorinated product formed to H+ consumed was 1:1. The implications of these results are discussed in terms of the known intraphagosomal pH changes that occur following neutrophil stimulation. We conclude that the O2-.-generating oxidase plays a dual role in the phagosome by simultaneously creating an oxidizing environment that optimizes pH-dependent microbicidal processes.