Conformational Transitions of Bovine β-Lactoglobulins A, B, and C

Abstract

Abstract The optical rotatory dispersion and proton-binding properties of bovine β-lactoglobulins A, B, and C have been examined as a function of pH. It was found that the b0 parameter remains constant between pH 2.5 and 10.5, while a0 undergoes large changes, from values of approximately -150 at pH 4 and below to -600 at pH 12. Two conformational changes occur in all three genetic variants, between pH 4 and 6, and pH 6.5 and 9.5, respectively. The first is accompanied by the liberation to titration of 1 cationic residue per chain in the C variant, with no similar effect in variants A and B. In the second transition an abnormal carboxyl per chain becomes ionizable in all three variants, as has been shown to occur in the A and B proteins.