EVIDENCE FROM AMINO ACID ANALYSIS FOR A RELATIONSHIP IN BIOSYNTHESIS OF GAMMA-CASEINS AND BETA-CASEINS

γ-Casein, like β-casein, is polymorphic as shown by gel electrophoresis. Two variants of γ-casein, A2 and B, have been isolated from samples of bovine casein genetically typed β-casein A2 and B. The β-caseins were also isolated from the same samples. By comparison of the composition of the proteins it was shown that γ-A2 differs from γ-B only in content of single residues of four amino acids and two substitutions, Ser/Arg and His/Pro are postulated. β-A2 differs from β-B in the same manner, implying a close relationship in the synthesis of these milk proteins. The γ-caseins differ considerably from the β-caseins in content of proline and phosphorus. Comparison of the composition of four polymorphs of β-casein indicated that, in addition to the Ser/Arg and His/Pro substitutions, a third, Glu/Lys, may occur in the β-casein variants. © 1969.