A classification of biologic lipids based upon their interaction in aqueous systems

Abstract

A classification of lipids is presented, based upon their physical properties in bulk aqueous systems and at the air‐water or oil‐water interface. This is supported by binary‐phase diagrams of the various classes of lipids in water. The interactions of the lipids of each class with a lipid of another class is illustrated by a series of different ternary‐phase diagrams of two lipids in water. The various types of association and the molecular relation of one lipid to another are indicated. The interaction of three classes of lipids with water is illustrated in two examples by quaternary‐phase diagrams of the three lipids in water. As an example of the application of these invitro studies, the composition of bile is correlated with a quaternary‐phase diagram cholesterollecithin‐bile salt‐water. The correlation shows that human bile behaves as a biologic four‐component system the physical state of which is entirely predictable from the quaternary‐phase diagram. Although bile is a special case, it is probable that the physical arrangement of the lipids in membranes, cellular organelles, lipoproteins, and adipose tissue can be suggested by studies of the interaction of lipid classes with themselves in water.