[The primary structure of bovine alpha s2 caseins].

The bovine alphas2-, alphas3-, alphas4- and alphas6-caseins [1] were isolated. The 4 proteins had the same amino-acid composition and C-terminal sequence, but different phosphorus contents. From a mixture of these proteins (designated as 'alphas2-complex') and from alphas3-casein a single and identical N-terminal sequence was obtained by Edman degradation. It seems therefore that the 4 proteins have the same peptide chain and only differ in their phosphorus content. For this reason we propose to modify the nomenclature of Annan and Mason [1] and to use in future the single term alphas2 to designate the caseins which have been previously called alphas2,alphas3,alphas4 and alphas6 by these authors. The study of the primary structure of the peptide chain, which has confirmed these results, was undertaken on the S-carboxymethylated alphas2-complex. From a cyanogen bromide digest and from a tryptic hydrolyzate of the alphas2-complex, 5 and 25 peptides were obtained respectively, both sets of peptides accounting for the whole peptide chain. Examination of the tryptic peptides containing methionine combined with the N- and C-terminal sequences of the alphas2-complex and some CNBr peptides, gave the order of the CNBr peptides, H.CN4--CN2--CN5--CN1--CN3.OH, which contain 4, 22, 115, 49 and 17 residues respectively. A partial sequence accounting for half of the peptide chain of the alphas2-complex is given. This peptide chain is likely composed of 207 amino-acid residues.