[Interaction of cholesterol with polypeptides and amino acids]

Using absorbance spectra at 185-225 nm, the interaction of cholesterol and its methyl and acetic esters with some amino acids, guanidine, metformine and two polypeptides-polyarginine and polylysine was studied. In aqueous and alcoholic media (pH 6-7) the largest shift of the absorption maximum in the presence of non-esterified cholesterol was observed in the compounds containing guanidinio groups (guanidine, metformine, arginine, polyarginine) and, in a lesser degree, the compounds containing epsilon-amino groups (lysine, polylysine). The cholesterol esters produced a marked shift in the absorption maxima of arginine, lysine, polyarginine and polylysine in a spirituous medium (as compared to an aqueous medium). During alpha-helization of polyarginine and polylysine (pH 10.5) the non-esterified cholesterol and also its methyl ester induced the highest shift in the absorption maximum of these polypeptides. The cholesterol interaction with the compounds containing the quanidinio and epsilon-amino groups can also be evidenced from the clarification of aqueous suspensions of cholesterol, its methyl ester and cholestane under effects of polylysine and especially polyarginine. The possibility of phospholipid-independent binding of cholesterol by proteins and the type of lipid protein interactions is discussed.