On the Dissociation of Bovine ,b-Lactoglobulins A, B, and C Near Ph 7

Abstract

Sedimentation-equilibrium studies are made of the moleoular weights of bovine ,B.laotoglobulins A, B, and C at pH 7·5. The order of dissooiation of dimer to monomer is A> B ~ C. The dissooiation oonstant (Kd) for A and B is 0·6 X 10-4 and 0·08x 10-4 mole 1-1 at 20°C, respeotively. The oonditions ohosen for these measurements are based on sedimentation velooity studies in the pH range 6-9. There is no ohange in sedimentation velooity behaviour following different times of standing at 20°C for pH < 7·5. The sedimentation patterns exhibit a single peak with some trailing on the solvent side. At low oonoentrations the plot of weight average sedimentation coefficient (,~) versus concentration (0) is in aocord with that of a rapidly dissociating system of monomer-dimer type. There are time-dependent aggregations above pH 8. Effects of changes in ionic strength and addition of methanol are considered.