Premiers elements de structure primaire des caseines αs2 bovines

[摘要]

The bovine α_s2-, α_s3-, α_s4- and α_s6-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 ‘α_s2-complex’) and from α_s3-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 α_s2 to designate the caseins which have been previously called α_s2, α_s3, α_s4 and α_s6 by these authors. The study of the primary structure of the peptide chain, which has confirmed these results, was undertaken on the S-carboxymethylated α_s2-complex. From a cyanogen bromide digest and from a tryptic hydrolyzate of the α_s2-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 α_s2-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 α_s2-complex is given. This peptide chain is likely composed of 207 amino-acid residues

[学科分类] 生物化学/生物物理