Binding of long chain fatty acids to beta-lactoglobulin.

Abstract

Abstractβ‐lactoglobulin (BLG), a bovine milk protein that is available commercially in crystalline form, binds long chain free fatty acids (FFA). The binding data were analyzed with a model containing one primary FFA binding site and a large number of weak secondary binding sites. At 37C and pH 7.4, the apparent association constant for binding of FFA to the primary site was of the order of 105 M−1 and that for binding to the secondary sites was approximately 103 M−1. The strength of binding was: palmitate > stearate > oleate > laurate. The affinity of BLG for palmitate increased as the pH of the incubation medium was raised from 6.5 to 8.7 and decreased as the ionic strength of the medium was raised. Palmitate binding was decreased in the presence of 6 M urea and when the protein either was exposed to elevated temperature or was acetylated prior to incubation. BLG took up methyl palmitate, cetyl alcohol, hexadecane and cholesterol to a lesser extent than FFA. Binding of FFA to BLG was associated with a small increase in the intensity of the fluorescent emission of the protein at 333 mμ. BLG can serve as an FFA acceptor or carrier in biological experiments. FFA released from adipose tissue during in vitro incubation was taken up by BLG. Net transfer of fatty acid to the incubation medium ceased when the molar ratio of FFA to BLG exceeded 1.1.14C‐1‐Palmitate bound to BLG was taken up by Ehrlich ascites tumor cells in vitro. At a given palmitate‐protein molar ratio, much more labeled fatty acid was taken up by these cells from media containing BLG than from those containing bovine albumin, apparently because FFA is bound less firmly to BLG than to albumin.