Micelle formation by bile salts. Physical-chemical and thermodynamic considerations

Abstract

Bile salts, which are soluble amphiphiles, possess a unique molecular structure when compared with typical detergent molecules. In water, bile salts form small aggregates called micelles. The behavior of bile salt micelles is quite different from micelles formed by detergents. Bile salt micelles are smaller, more highly charged and of different structure than detergent micelles. Bile salts form mixed micelles with a variety of other soluble and insoluble lipidic substances. While bile salts increase slightly the solubility of relatively nonpolar molecules (such as cholesterol or fatty acids), they have a striking capacity to render soluble certain important insoluble molecules of biological importance such as phospholipids and monoglycerides. In fact as little as 1 mole of bile salt can solubilize 2 moles of lecithin. Solubilization takes place in mixed bile salt micelles of unique structure and properties. These mixed micelles incorporate very appreciable amounts of insoluble molecules, such as fat-soluble vitamins