Sedimentation equilibrium in reacting systems. VII. The temperature-dependent self-association of β-lactoglobulin A at pH 2.46

The self-association of β-lactoglobulin A in 0.2 m glycine buffer (pH 2.46 at 23.5 °C) has been studied by low speed sedimentation equilibrium experiments at 11, 16, 20, 25 °C. In all four sets of experiments the concentration dependence of the apparent weight average molecular weight, M wa, was indicative of a nonideal self-association. The association decreased with increasing temperature. Several models to describe the observed self-association were tested, and a monomer-dimer association describes the data best. Values of the association equilibrium constant, K 2, and the second virial coefficient, BM 1, are reported at each temperature. Values of the thermodynamic functions, ΔG °, ΔH °, and ΔS °, are also reported for these experiments.