Some Physical Properties of Bile Acids and Their Amino Acid Conjugates

Some Physical Properties of Bile Acids and Their Amino Acid Conjugates 

Chemically, the bile acids are hydroxylated derivatives of cholanic acid, a tetracyclic steroid acid of 24 carbon atoms. The acids occur in nature largely as the water-soluble sodium salts of peptide conjugates of glycine and taurine. The free acids are liberated by saponification or specific enzyme hydrolysis. The chemistry of the bile acids has been reviewed in Chapter 1 of this volume (1). In view of their highly polar nature, special attention is called to the recent discovery of the cholic acid conjugates of ornithine (2, 3) and the 3a-sulfate esters of glycolithocholic and taurolithocholic acids (4). 

At low concentrations, the bile acids are freely soluble in water and yield molecular solutions. The concentration at which molecular solubility is reached is termed the critical micelle concentration. Above this concentration, aggregation of the molecules occurs and micelles are formed. Hofmann and Small (6) have summarized the effects of temperature, electrolyte concentration, impurities, and the pH of the solution upon the critical micelle 

TABLE I. Critical Micelle Concentrations of Some Bile Salts (Moles/liter)  

TABLE II. True Dissociation Constants and Values of Bile Acids  

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