Identity of cow _β-Lactoglobulin 'B' and buffalo _β-Lactoglobulin

Abstract

Since the demonstration by Aschaffenburg and Drewry that β -lactoglobulins of cow's milk occur in two different forms, 'A' and 'B', many attempts have been made to find the differences in the primary structure of these two protein types. The differences between the two genetic species have been shown to lie in the contents of four amino-acids, namely, aspartic acid, valine, glycine and alanine, β -lactoglobulin A having one more residue each of aspartic acid and valine and one less residue each of glycine and alanine than β -lactoglobulin B per half molecule. Likewise, chymotryptic peptide pattern analyses of sulphonated β -lactoglobulins A and B have indicated similarity of peptide pattern except for a single pair in which one aspartic acid residue in 'A' is replaced by one glycine residue in the corresponding 'B' peptide. Information regarding the buffalo β -lactoglobulin, on the other hand, is scanty. It has been reported that cow β -lactoglobulin B and buffalo β -lactoglobulin have approximately the same molecular weight and are practically indistinguishable in crystal form, electrophoresis, sedimentation and ultra-violet absorption.