Para-phenylazophenyl isothiocyanate as a possible reagent in the N-terminal amino acid sequence determination of proteins

Buffalo alpha S1-casein; its terminal residues and amino acid composition

Buffalo alpha S1-casein was treated with carboxypeptidase-A to determine the C-terminal amino acid residue, which was - leucine-tryptophan. The Sakaguchi reagent was used to confirm arginine as the N-terminal amino acid. The colored p-phenylazophenyl thiohydantoins of tryptophan and arginine released from C- and N-terminals respectively were quantitatively estimated and from this molecular weights of buffalo alpha S1 casein were calculated and found to be 26,300 and 26,100 respectively.

First fifteen amino acid residues in buffalo alpha S 1-casein from the N-terminal end

Conventional Edman degradation techniques with phenyl isothiocyanate and p-phenylazophenyl isothiocyanate were used to determine the first 15 amino-terminal amino acid residues in buffalo alpha S 1-casein. The results were compared to those of bovine alpha S 1-casein.