Lipid binding properties of fatty acid binding protein isolated from mouse liver

The present studies were designed (1) to examine the lipid composition of two protein fractions from mouse liver cytosol, and (2) to correlate this composition with the previously observed transfer and lipid binding properties of a protein named fatty acid binding protein. In the first part of this study, the ability of the cytosolic protein fractions to bind fatty acids was studied by gel filtration chromatography of cytosol in the presence of [1-14C] oleic acid. Two fractions with affinity for oleic acid were identified. The amount of phospholipids, cholesterol and cholesterol esters found in the low molecular weight protein fraction was significantly higher than that present in the protein fraction with high molecular weight. When mouse liver microsomes prelabeled with [1-14C] stearate were incubated with the protein fraction enriched in fatty acid binding protein, the protein removed radioactivity from the neutral rather than from the polar lipid fraction. Such an effect was drastically reduced when the protein was presaturated with oleic acid. The results suggest that fatty acid binding protein may bind cholesterol and its esters in addition to free fatty acids.