Composition of Bovine γ-Caseins A1 and A3, and Further Evidence For a Relationship in Biosynthesis of γ- and β-Caseins

Abstract Two variants, A 1 and A 3 , of γ - and β -caseins were isolated from samples of bovine milk which were typed as homozygous for β -casein A 1 or A 3 . γ - and β -Caseins A 1 and A 3 differ in amino acid composition by two residues of histidine and the data suggest that the same substitutions, His/Gln and His/Gln or His/Pro distinguish the γ - and β -variant pairs. γ - β -casein polyrnorphs A l , A 2 , A 3 and B all have a common C-terminal sequence -Ile-Ile-Val OH and they show similar chymotryptic peptide maps. They differ in their N-terminal amino acids: arginine for β -caseins and lysine for γ -caseins. γ -Casein is smaller than β -casein by about 28 amino acid residues. It is possible that γ -casein is identical with a large portion of β -casein.