Sedimentation equilibrium studies on betalactoglobulin C at acid pH

Abstract

The self-association of [beta]-lactoglobulin C at acid pH has been studied in glycine buffers and acetate buffers by sedimentation equilibrium. In glycine buffers, pH ca. .25, the self-association was studied by low and high speed sedimentation equilibrium experiments at four temperatures, 10, 16, 20 and 25 [degrees] C. One buffer had an ionic strength of 0.1 and the other had an ionic strength of 0.2. With either buffer, the concentration dependence of the apparent weight average molecular weight, M[subscript wa], was characteristic of a nonideal self-association. Like its genetic variants, [beta]-lactoglobulins A and B, the self-association of [beta]-lactoglobulin C increased with decreasing temperature. At the same temperature, the association was always stronger in the buffer having the higher ionic strength. Several models were used to test the self-association, and a monomer-dimer self-association seemed to describe the self-association best with either buffer. Values of the association equilibrium constant, K[subscript 2], ranged from 27.2 to 5.9 dl/g at I = 0.1 and from 60.1 to 27.2 dl/g at I = 0.2.