Structure primaire de la caséine αS1 bovine

A previous paper described the amino acid composition of the fragments resulting from selective cleavage of the bovine αS1‐casein polypeptide chain at arginyl bonds after blocking the lysyl residues by maleic anhydride. The fragment Tm2, which is 48 residues long, represents the COOH‐terminal part of the αS1‐casein chain, according to the following observations: (a) it is devoid of arginine; (b) only the peptide Tm2 is coloured by the Ehrlich reagent specific for Tryptophane; (c) the two amino acids released by carboxypeptidase A (successively Tryptophane and Leucine) are those of the COOH‐terminal end of αS1‐casein. The complete sequence of this large COOH‐terminal peptide obtained from αS1‐casein C was determined by classical methods, using endopeptidases to produce smaller peptides, then exopeptidases and the Edman sequential degradation procedure for establishing the amino acid sequence of these peptides. A part of this work has been published in a previous communication reporting the location, at the eighth position from the COOH‐terminal end, of the substitution Gly/Glu between the genetic variants αS1C and αS1B.