The effect of pressure and the volume of activation on the monovalent cation and glucose permeabilities of liposomes of varying composition

Abstract

Measurement of the cation permeability of phospholipid microvesicles as a function of pressure confirmed that a single rate-determining step occurred in each case. The volume of activation was 20 ml-mole minus 1 for Na+ and K+, and about 40 ml-mole minus 1 for valinomycin-mediated K+ permeability. It was virtually independent of membrane composition. The results were explained in terms of Träuble's theory of kink-substrate dissociation at the membrane interface involving possible 2gl and 2g2 kink isomers. The volume of activation for D-glucose was 37 ml-mole minus 1, which was not significantly different from that for any of the valinomycin-mediated K+ permeabilities. However, other data suggest that the rate-limiting steps for the sugar and cation permeabilities are not the same.