Table 1.

Proton conduction through water, gramicidin, and H_V1 channels

Property	Bulk water	Gramicidin	HV1
Selectivity (${\mathit{P}}_{{\mathrm{H}}^{+}}$/${\mathit{P}}_{{\mathrm{Na}}^{+}}$)	71	38–1502	>106–108 (3)
Deuterium isotope effect (${\mathit{I}}_{{\mathrm{H}}^{+}}$/${\mathit{I}}_{{\mathrm{D}}^{+}}$)	1.414	1.355	1.96
Activation energy (kcal mol−1)	2.67	4.88	18–279

The activation energy is for proton permeation through open channels. The temperature dependence of gramicidin includes measurements on dioxolane‐linked channels. ¹Robinson & Stokes, 1959; ²Myers & Haydon, 1972; ³DeCoursey, 2003; ⁴Lewis & Doody, 1933; ⁵Akeson & Deamer, 1991; Chernyshev et al. 2003; ⁶DeCoursey & Cherny, 1997; ⁷Robinson & Stokes, 1959; ⁸Akeson & Deamer, 1991; ⁹DeCoursey & Cherny, 1998. This table was reprinted with minor changes from: DeCoursey TE. (2008). Voltage‐gated proton channels: what's next? J Physiol 586, 5305–5324.