Patent ID: 7125685

Claim:
A method for identifying a protein, the method comprising the steps of: (a) separating the protein from other proteins; (b) digesting the protein, thereby forming first proteolytic peptides; (c) acquiring a monoisotopic mass distribution spectrum of the first proteolytic peptides and acquiring the m/z values for the first proteolytic peptides; (d) introducing at least one amino acid 100% labeled with at least one stable isotope into a cell that expresses a protein, and wherein the cell is induced to express the protein comprising the at least one amino acid 100% labeled in a sequence-specific manner; (e) separating the protein bearing the at least one labeled amino acid from other proteins; (f) digesting the protein bearing the at least one labeled amino acid, thereby forming second proteolytic peptides; (g) acquiring the monoisotopic mass distribution spectrum of the second proteolytic peptides and acquiring the m/z values for the first proteolytic peptides; (h) comparing the monoisotopic mass distribution spectrum of the second proteolytic peptides with the monoisotopic mass distribution spectrum of the first proteolytic peptides to determine the amino acid composition of the first proteolytic peptides and the second proteolytic peptides, whereby the protein is identified from the m/z values of the first proteolytic peptides and the m/z values of the second proteolytic peptides and the amino acid composition of the first proteolytic peptides and the second proteolytic peptides.