Multiple classes of binding sites for palmitic acid on the fatty acid-binding protein molecule

Binding characteristics of fatty acid-binding protein (FABP) toward palmitic acid were studied. On the analysis of the interaction between FABP and [3H]palmitic acid over a wide range of concentrations of the fatty acid, at least three saturation plateaux were observed. By Scatchard-plot analysis, it appeared that FABP possesses three classes of binding sites for palmitic acid with different affinities [Kd1 = 1 x 10(-6) M (N = 1), Kd2 = 4 x 10(-6) M (N = 2), Kd3 = 2 x 10(-5) M (N = 10)]. Results of both sedimentation analyses and chromatofocusing of FABPs labeled with various concentrations of [3H]palmitic acid suggested that the FABP used was homogeneous. These results indicate that several classes of binding sites for palmitic acid with different affinities are present on the FABP molecule.