Patent ID: 7402407

Claim:
A method for identifying a position of at least one post-translationally modified (PTM) amino acid residue in at least one peptide, comprising a) treating a sample comprising at least one peptide with at least one reagent that can chemically modify a PTM amino acid residue of a peptide, wherein the PTM amino acid residue comprises a phosphorylated amino acid residue, whereby, when a peptide comprises at least one PTM amino acid residue, a peptide comprising at least one chemically modified amino acid residue is generated, wherein the peptide is susceptible to cleavage by a proteolytic agent at the position of the chemically modified amino acid residue, and wherein the peptide is not susceptible to cleavage by the proteolytic agent at the position of the PTM amino acid residue prior to chemically modifying the PTM amino acid residue; b) contacting the peptide comprising the chemically modified amino acid residue with the proteolytic agent, whereby the peptide is cleaved at the position of the chemically modified amino acid residue to produce cleavage products indicative of the position of a PTM amino acid residue in the peptide; and c) determining the mass of one or more of the cleaved products, thereby identifying the position of at least one PTM amino acid residue in at least one peptide.