The gp91^phox Component of NADPH Oxidase Is Not the Voltage-gated Proton Channel in Phagocytes, but It Helps

During the "respiratory burst," the NADPH oxidase complex of phagocytes produces reactive oxygen species that kill bacteria and other invaders (Babior, B. M. (1999) Blood 93, 1464-1476). Electron efflux through NADPH oxidase is electrogenic (Henderson, L. M., Chappell, J. B., and Jones, O. T. G. (1987) Biochem. J. 246, 325-329) and is compensated by H⁺ efflux through proton channels that reportedly are contained within the gp91^phox subunit of NADPH oxidase. To test whether gp91 ^phox functions as a proton channel, we studied H⁺ currents in granulocytes from X-linked chronic granulomatous disease patients lacking gp91^phox (X-CGD), the human myelocytic PLB-985 cell line, PLB-985 cells in which gp91^phox was knocked out by gene targeting (PLB_KO), and PLB-985 knockout cells re-transfected with gp91 ^phox (PLB₉₁). H⁺ currents in unstimulated PLB_KO cells had amplitude and gating kinetics similar to PLB ₉₁ cells. Furthermore, stimulation with the phorbol ester phorbol 12-myristate 13-acetate increased H⁺ currents to a similar extent in X-CGD, PLB_KO, and PLB₉₁ cells. Thus, gp91^phox is not the proton channel in unstimulated phagocytes and does not directly mediate the increase of proton conductance during the respiratory burst. Changes in H⁺ channel gating kinetics during NADPH oxidase activity are likely crucial to the activation of H⁺ flux during the respiratory burst.