Self-association of beta-lactoglobulin c in acetate buffers

The self-association of beta-lactoglobulin C at pH 4.65 (23 degrees C) in acetate buffer has been studied at various temperatures, 10, 16, 20 and 25 degrees C, by a series of sedimentation equilibrium experiments. Two different buffers were used. Buffer I with an ionic strength of 0.1 consisted of 0.1M acetic acid and 0.1M sodium acetate; buffer II had 0.1M KCl in addiation so that its ionic strength was 0.2. The variation of the apparent weight average molecular weight, Mwa, with the total solute concentration, c, was characteristic of a self-association. In contrast to the behavior of beta-lactoglobulin A in acetate buffer, the association of beta-lactoglobulin C did not proceed beyond dimer. Furthermore, within the experimental error, the self-association of beta-lactoglobulin C was independent of temperature and ionic strength; all experimental data could be put on the same Mwa (or M1/Mwa) vs. c plot! Several models were used to test the self-association, and a monomer--dimer association with K2 = 2.10 X 10(3) dl/g and BM1 =- 1.2 X 10(-2) dl/g seemed to give a good description of the M1/Mwa vs. c curve.