The interaction of polypeptide components of human high density serum lipoprotein with detergents.

The cationic detergent tetradecyltrimethylammonium ion interacts with four binding sites on the surface of AI polypeptide from human serum high density lipoprotein and 10 sites on the AI1 polypeptide with association constants of 2 X lo4 and 1 x lo4 liters per mole, respectively. The sites on AI appear to be primarily hydrophobic in that the anionic detergent sodium dodecyl sulfate binds to the same number of sites with the same association constant as the cationic amphiphile. Cooperative binding and a concomitant protein conformational change at higher free concentrations of ligand ( >10e4 M) are observed for both AI and AI1 with these two detergents as well as with deoxycholate. It is suggested that this altered protein state may differ from those observed for water-soluble proteins in high concentrations of tetradecyltrimethylammonium ion or dodecyl sulfate.