A Spin Label Study of the Influence of Cholesterol on Egg Lecithin Multibilayers

Abstract

A detailed electron spin resonance study of a cholestane spin label in hydrated egg lecithin multibilayers of variable cholesterol content is presented. Several theoretical models are proposed in an attempt to explain the observed electron spin resonance spectra for the egg lecithin–cholesterol multibilayer system; we conclude that the most probable model is that of restricted random walk of individual spin labels where the amplitude of the random walk decreases from about 46° at 0 mol% cholesterol content to a minimum of 17° at 55 mol% cholesterol. Also, as the cholesterol content of the multibilayers increases, so the rate of random walk decreases from rapid to intermediate on the electron spin resonance time scale. The results clearly indicate that cholesterol is able to order egg lecithin films, orientating all molecules towards a normal to the surface of the film and decreasing their mobility. The condensing and stiffening influence of cholesterol in phospholipids is undoubtedly one of its major roles in biological membranes.