INCORPORATION OF STEROID MOLECULES INTO LECITHIN SOLS BETA-LIPOPROTEINS AND CELLULAR MEMBRANES

The dispersion of various steroids in aqueous solution with ovolecithin was investigated and the following molar ratios of lecithin to steroid obtained: cholesterol, 1:1; 7‐dehydrocholesterol, 13.3:1; ergosterol, 13.1:1; sitosterol, 2.0:1; sterophenol 4.2:1; cholesta‐4,6‐dien‐3‐one, 2.0:1; cholest‐4‐en‐3‐one, 1.7:1. The cholesterol contents of sterol‐depleted cellular membranes can be restored to their original level by incubation with plasma or an equimolar dispersion of cholesterol and ovolecithin, in the presence of 10% dimethylsulphoxide (v/v). Cholesta‐4,6‐dien‐3‐one, cholest‐4‐en‐3‐one, 7‐dehydrocholesterol and sterophenol can exchange readily with the cholesterol erythrocyte ghosts and can replace cholesterol molecules removed from the membrane. Ergosterol can do so only to a very limited extent. 7‐Dehydrocholesterol exchanges between rat erythrocyte ghosts and human piasma β‐lipo‐proteins in the same way as cholesterol. Cholesta‐4, 6‐dien‐3‐one and cholest‐4‐en‐3‐one also exchange but, in addition, there is a net uptake of these steroids by β‐lipoproteins. The extra steroid entering the lipoproteins is probably dissolved in the hydrophobic core of the latter. The exchange of cholesta‐4,6‐dien‐3‐one between erythocyte ghosts and lecithin/steroid dispersions or β‐lipoproteins is much more rapid than that of cholesterol. The rate of exchange of the dienone, like that of cholesterol, is increased by the addition of a small quantity of dismethylsulphoxide to the medium. Copyright © 1968, Wiley Blackwell. All rights reserved