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

Two variants, A 1 and A s, of 2/-and /3-caseins were isolated from samples of bovine milk which were typed as homozygous for /3-casein A 1 or A s. y-and /3-Caseins A x and A 3 differ in amino acid composition by two residues of histidine and the data suggest that the same substitutions, His/Gin and His/Gin or His/Pro distinguish the y-and/3-variant pairs, y-/3-casein polymorphs A x, A 2, A s 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 /3-caseins and lysine for y-caseins, y-Casein is smaller than /3-casein by about 28 amino acid residues. It is possible that y-casein is identical with a large portion of/3-casein.