Hydrophobic interactions of the apo-Gln-I polypeptide component of human high density serum lipoprotein.

Apo-Gln-I, the major polypeptide component of human serum high density lipoprotein, has four noninteracting hydrophobic sites which associate with alkanes, anionic detergents, and cationic detergents. Hexane and octane bind to these sites with association constants of 6.8 times 10-2 and 1.8 times 10-4 liters/mol, respectively, and compete with the anionic detergent, sodium dodecyl sulfate (C12OSO3-minus), at low detergent ligand binding ratios (i.e. smaller than or equal to 1.0 mol of C12OSO3-minus per mol of protein). At higher detergent binding ratios (larger than 2 mol of C12OSO3-minus per mol of protein) the polypeptide cooperatively binds alkanes and a conformational change is induced.