Voltage-gated proton (hydrogen) channels play an important role in cellular defense against acidic stress. They are unique among ion channels with respect to their extremely high selectivity, marked temperature dependence, and unitary conductance, which is 3 orders of magnitude lower than that of most other ion channels. NOX1 is a homolog of the catalytic subunit of the superoxide-generating NADPH oxidase of phagocytes, gp91phox. Two transcript variants encoding different isoforms have been found for this gene.