Premiers elements de structure primaire des caseines αs2 bovines

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Abstract
The bovine αs2-, αs3-, αs4- and αs6-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 ‘αs2-complex’) and from αs3-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 Manson [1] and to use in future the single term αs2 to designate the caseins which have been previously called αs2, αs3, αs4 and αs6 by these authors. The study of the primary structure of the peptide chain, which has confirmed these results, was undertaken on the S-carboxymethylated αs2-complex. From a cyanogen bromide digest and from a tryptic hydrolyzate of the αs2-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 αs2-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 αs2-complex is given. This peptide chain is likely composed of 207 amino-acid residues