A comparison of bovine alpha-lactalbumin A and B of Droughtmaster

It is shown that either or both of two α-lactalbumins (designated A and B) may occur in the milk of Droughtmaster cattle. Their occurrence is genetically determined. The B variant has the same amino acid composition as the sole α-lactalbumin occurring in the milk of European breeds and the A variant differs from the B variant having one less arginine residue (0 vs. 1) and one more glutamine residue. There are two peptides in the map of the B variant that are not present in the map of A, and one peptide in B not present in A. These difference peptides have been isolated and their amino acid composition and electrophoretic mobility determined. One peptide has been subjected to Edman degradation. The data are considered in the light of the known partial sequence of α-lactalbumin of European breeds. It is concluded tentatively that the substitution of glutamine in A for arginine in B occurs at residue No. 10.