Studies on the mode of action of excess of vitamin A. 9. Penetration of lipid monolayers by compounds in the vitamin A series

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Abstract
Vitamin A1 alcohol forms a mono-molecular film that has a collapse pressure of 22.5 dynes/cm at an air-water interface. This collapse pressure is greater than that of the films formed by a number of closely related derivatives. Compounds in the vitamin A series are able to penetrate a monolayer of lecithin-cholesterol held at 30 dynes/cm and constant area. Vitamin A1 alcohol, vitamin A1 acid and vitamin A2 alcohol cause the greatest increases in surface pressure on penetration of the lipid film. Vitamin A1 alcohol is the only compound of those studied that is able to cause both a large increase in surface pressure at constant area and also a large increase in area of a lecithin-cholesterol film at a constant surface pressure of 30 dynes/cm. The effect of temperature on penetration of a lecithin-cholesterol film by vitamin A1 alcohol was investigated. Vitamin A1 alcohol interacts more strongly with lecithin than with cholesterol. The penetration of a film of lecithin-cholesterol by vitamin A1 alcohol indicates that penetration of lipo-protein membranes may be an initial step in certain actions of the vitamin; the molecular specificity observed in the experiments with lipid films may be the basis of the molecular specificity observed in many of the functions of vitamin A.