Lee's transient protonic capacitor cannot explain the surface proton current observed in bacteriorhodopsin purple membranes

Recently in this Journal, James Lee employed his transmembrane electrostatically localized proton (TELP) hypothesis and the notion of a transient protonic capacitor to explain the force holding protons at the surface of bacteriorhodopsin purple membrane fragments. Here we show that purple membrane fragments cannot maintain the requisite transient non-zero transmembrane potential, and even if they could, it would not support the surface proton current moving from the P side to the N side that was reported by Heberle et al. (Nature, 1994). Currently accepted models explain the force keeping protons at the membrane surface by invoking the unusual structure of water at the interface which serves to stabilize the proton (energy well) and/or raise the activation ∆G‡ (energy barrier) for release to the bulk phase. Any future invocations of TELP should be required to include experimental measurements carried out at the surfaces of lipid bilayer membranes and/or biological membranes.

A critique of the capacitor-based "Transmembrane Electrostatically Localized Proton" hypothesis

In his Transmembrane Electrostatically Localized Proton hypothesis (TELP), James W. Lee has modeled the bioenergetic membrane as a simple capacitor. According to this model, the surface concentration of protons is completely independent of proton concentration in the bulk phase, and is linearly proportional to the transmembrane potential. Such a proportionality runs counter to the results of experimental measurements, molecular dynamics simulations, and electrostatics calculations. We show that the TELP model dramatically overestimates the surface concentration of protons, and we discuss the electrostatic reasons why a simple capacitor is not an appropriate model for the bioenergetic membrane.