Polyacrylamide gel eleetrophoresis or starch gel e/ectrophoresis at pH 3 demonstrafes that the fi-easein type A, as classified at pH 9, actually consists of three species, A 1, A 2, and A s. Chromatography on cellulose phosphate has been used to sepaa'ate an AS/B fl-casein into its constituents. Amino acid analyses and end group analyses of fl-caseins A s were compared with those of the other genetic variants, A 1 and A 2 fi-easeins. The three variants, A 1, A 2, and A 3, have 6, 5, and 4 histidine residues per molecule of ,~24,000 Daltons. The analytical data indicate a substitution of proline for histidine.
No takes yet. Share an insight, caveat, or question.
Kopfler et al. (1969) studied this question.