FIG. 3.

Superoxide generation in a signaling endosome. Activated NADPH oxidase (Nox 2) transfers an electron from cytoplasmic NADPH to O₂ in the lumen of the endosome to generate O₂^•−. The O₂^•− can exit the endosome through a chloride channel (ClC) (A) or dismute to H₂O₂ (B–D). Charge compensation theoretically can be provided by efflux of O₂^•− (A), influx of H⁺ through a proton channel (B), efflux of Cl⁻ through a Cl⁻ channel (C), or exchange of luminal Cl⁻ for cytoplasmic H⁺ through an H⁺/Cl⁻ antiporter (D). Modified with permission from (32).