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

Abstract

Two variants, A1 and A3, of γ- and β-caseins were isolated from samples of bovine milk which were typed as homozygous for β-casein A1 or A3. γ- and β-Caseins A1 and A3 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 Al, A2, A3 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. © 1972, American Dairy Science Association. All rights reserved.