Micelle Formation in Aqueous Solutions of Bile Salts

The solubility of fatty acids and cholesterol in bile does not appear to be due to the formation of soluble compounds of the choleic acid type. The bile is made up chiefly of the conjugated bile salts and such compounds with conjugated bile acids or salts have not been isolated (1). It is generally agreed that the solution of oils in aqueous solutions of soaps is associated with the micelle formation of the soap, the oil being dissolved, most likely, in the lipid center of the micelle (2-4). The bile salts are similar to the soaps in that they consist of a relatively large hydrophobic group and an ionic group. They might be expected also to form micelles and thus to be able to take up water-insoluble substances in a manner comparable to that of the soaps. Bashour and Bauman (5) were unable to find a sharp change of slope in the equivalent conductivity-concentration curve of sodium desoxycholate, usually taken as an indication of micelle formation, although freezing point determinations on the more concentrated solutions indicated some degree of aggregation. It seemed likely that measurement of the osmotic coefficient as well as of the equivalent conductivity at various concentrations would offer some evidence as to the state of aggregation of bile salts.