The gp91phox Component of NADPH Oxidase Is Not a Voltage-gated Proton Channel

During the “respiratory burst” in phagocytes, NADPH oxidase helps kill microbes by producing superoxide anion, O 2 . As illustrated in the cartoon in Fig. 1, the NADPH oxidase complex has several components. In unstimulated cells, four components (p67 phox , p40 phox , p47 phox , and a G protein, Rac) are located in the cytosol, and gp91 phox and p22 phox are membrane bound. Upon stimulation by bacteria, PMA (phorbol ester), or chemotactic peptides, the complex assembles and begins to generate O 2 . This is accomplished by transporting electrons from NADPH inside the cell, across the cell membrane to reduce extracellular O 2 to O 2 . Without charge compensation, the electron efflux in a human eosinophil would depolarize the membrane by 12 V/s, and this opposing voltage would shut down the oxidase within 20 ms. Henderson et al. (1987, 1988a,b) demonstrated that electrogenic H efflux in human neutrophils compensates for electrogenic electron translocation through the NADPH oxidase complex. The consensus is that the electron current is balanced by proton efflux mediated by voltage-gated proton channels. A recent suggestion that K efflux contributes 6% of the total charge compensation (Reeves et al., 2002), still leaves 94% of the job to proton channels. The molecular identity of these H channels is not known. A variety of evidence has been interpreted to suggest that gp91 phox can function as a proton channel, but critical examination of the evidence shows that this is not the case. The evidence on both sides falls into two general categories: heterologous expression studies and circumstantial evidence. The heterologous expression studies claiming proton channel function for gp91 phox