Kinetics and thermodynamics of the formation of mixed micelles of egg phosphatidylcholine and bile salts.

The kinetics of dissolution of dispersions of egg phosphatidylcholine (lecithin) by bile salts was studied by observing the decrease in turbidity as mixed micelles of lecithin and bile salt were formed. The rate of dissolution of lecithin corresponding to the formation of mixed micelles was studied in the presence of dihydroxy bile salts, sodium deoxycholate, sodium chenodeoxycholate, sodium ursodeoxycholate, and one trihydroxy bile salt, sodium cholate. The rate of dissolution of lecithin and mixed micelle formation decreased in the order: chenodeoxycholate greater than deoxycholate greater than cholate greater than ursodeoxycholate. Kinetic solvent isotope studies in D2O, along with measurement of enthalpies of mixed micelle formation both in H2O and D2O, appear to indicate that the formation and stabilization of mixed micelles is related to "hydrophobicity" as estimated by high performance liquid chromatography retention factors.