NONELECTROLYTE PERMEABILITY OF LIPID BILAYERS: STRUCTURE-FUNCTION RELATIONSHIPS IN MODEL MEMBRANE SYSTEMS
ORBACH, ELI M.
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The permeability of lecithin bilayer membranes to nonelectrolytes is in reasonable agreement with Overton's Rule. That is, P(,d) (alpha) DK(,hc) where P(,d) is the permeability coefficient of a solute through the bilayer, K(,hc) is its hydrocarbon:water partition coefficient, and D is its diffusion coefficient in bulk hydrocarbon. The partition coefficients are by far the major determinants of the relative magnitudes of the permeability coefficients; the diffusion coefficients make only a minor contribution. We note that the recent emphasis on theoretically calculated intramembranous diffusion coefficients (D(,m)'s) has diverted attention from the experimentally measureable and physiologically relevant permeability coefficients (P(,d)'s) and has obscured the simplicity and usefulness of Overton's Rule.