Effect of the Surface Potential on Membrane Enzymes and Transport

Abstract

The surface charge of biological membranes is produced by dissociable groups of membrane constituents, mainly phospholipids and proteins. The surface potential (Ψ_o) is related to the surface charge density (6) according to the Gouy-Chapman equation which, when simplified for a symmetric electrolyte, is

$${{\varphi }_{o}}=\frac{2RT}{zF}\arcsin h\left[ 6{{\left( 8RT{{\varphi }_{o}}{{\varphi }_{r}}C \right)}^{-\frac{1}{2}}} \right]$$

(1)

where R is the gas constant, T is the absolute temperature, F is the Faraday constant, C denotes the concentration of the electrolyte, and z is its valency, _∈o is the permittivity of the vacuum, and _∈r is the relative permittivity (dielectric constant) of the medium. Because of electric attraction or repulsion, the concentration of ions in the immediate vicinity of the membrane surface (C_o) is different from that in the bulk solution (C_∞), as described by the Boltzmann distribution

$${{C}_{o}}={{C}_{\infty }}\exp \left( -zF{{\varphi }_{o}}/RT \right)$$

(2)