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Amino Acid Composition of Chromatographically Separated ß-Casein A³

Eastern Utilization Research and Development Division, USDA, Philadelphia, Pennsylvania 19118
Dairy Cattle Research Branch, Animal Husbandry Research Division, USDA, Beltsville, Maryland 20705

ABSTRACT

Polyacrylamide gel electrophoresis or starch gel electrophoresis at pH 3 demonstrates that the ß-casein type A, as classified at pH 9, actually consists of three species, A¹, A², and A³. Chromatography on cellulose phosphate has been used to separate an A³/B ß-casein into its constituents. Amino acid analyses and end group analyses of ß-caseins A³ were compared with those of the other genetic variants, A¹ and A² ß-caseins. The three variants, A¹, A², and A³, have 6, 5, and 4 histidine residues per molecule of ~24,000 Daltons. The analytical data indicate a substitution of proline for histidine.

¹ National Research Council-Agricultural Research Service Postdoctoral Research Associate. Present address: Gulf Coast Marine Health Sciences Laboratory, U.S. Publie Health Service, Dauphin Island, Alabama 36528.