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

From the ¹ From the Eastern Regional Research Laboratory, Eastern Utilization Research and Development Division, Agricultural Research Service, United States Department of Agriculture, Philadelphia, Pennsylvania 19118

The optical rotatory dispersion and proton-binding properties of bovine ß-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.

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