Bovine β-lactoglobulin is dimeric under imitative physiological conditions: Dissociation equilibrium and rate constants over the pH range of 2.5-7.5

Abstract

The oligomerization of β-lactoglobulin (βLg) has been studied extensively, but with somewhat contradictory results. Using analytical ultracentrifugation in both sedimentation equilibrium and sedimentation velocity modes, we studied the oligomerization of βLg variants A and B over a pH range of 2.5-7.5 in 100 mM NaCl at 25°C. For the first time, to our knowledge, we were able to estimate rate constants (koff) for βLg dimer dissociation. At pH 2.5 koff is low (0.008 and 0.009 s-1), but at higher pH (6.5 and 7.5) koff is considerably greater (>0.1 s-1). We analyzed the sedimentation velocity data using the van Holde-Weischet method, and the results were consistent with a monomer-dimer reversibl..