Effect of lysolecithin on the binding of 1-anilino-8-naphthalene sulfonate to apoHDL, apoA-I or apoA-II from human serum high density lipoprotein.

Abstract

The binding of 1-anilino-8-naphthalene sulfonate to human serum high density apolipoprotein and to apoA-I and apoA-II which are major protein components of high density apolipoprotein was measured by a fluorometric method. The maximum number of 1-anilino-8-naphthalene sulfonate bound to high density apolipoprotein was about 950 mumol per g of protein, and those to apoA-I and apoA-II were 27 and 13 mol per mol of protein (there values correspond to 964 for apoA-I and 765 for apoA-II in mumol per g of protein), respectively. After preincubation of apolipoprotein with lysolecithin (less than 10 microM), the binding affinities for the dye increased twice or more with all the proteins, but the maximum binding numbers changed little. With apoA-I, two mol of the dye were bound with high affinity and lysolecithin did not compete with the dye for the binding sites. The fluorescence intensity of tryptophanyl residues of apoA-I was changed by incubation with lysolecithin at concentrations lower than the critical micellar concentration. These results indicate that the binding of lysolecithin molecules to apoA-I or other proteins makes the protein conformation more suitable for the binding of hydrophobic ligands.