Assignment of phosphorylation sites in buffalo beta-casein by fast atom bombardment mass spectrometry

Fast atom bombardment mass spectrometry has been applied to the localization of phosphorylation sites in buffalo beta-casein. Two complementary strategies of identification are described. Phosphorylated residues in the tryptic peptide Tp 1 have been assigned by measuring the masses of peptide fragments obtained by enzymatic degradations. The phosphoserine residue in peptide Tp 2 has been identified by determining the intact molecular weight and confirmed by partial sequence information. This rapid and sensitive procedure appears of a great interest in structural studies of a wide range of post-translational modifications in proteins.