Patent ID: 7108985

Claim:
A method for analyzing a protein sample using a subset of peptides produced from the protein sample; the method comprising: (a) first digesting proteins in the protein sample to produce a set of digested peptides, the set including one or more peptides having an amino terminal serine or an amino terminal threonine; (b) providing a tagging moiety having the formula: R-L-B wherein R is a reactive group that reacts with the amino terminal serine or an amino terminal threonine of the digested peptides, L is a linker group containing zero or more atoms, and B is a group that can selectively bind to a capture reagent; (c) reacting the set of peptides with the tagging moiety to provide a subset of tagged peptides; (d) contacting the subset of tagged peptides with the capture reagent to provide captured tagged peptides; (e) releasing at least peptide portions of the captured tagged peptides from the capture reagent to provide released modified peptides; and (f) analyzing the protein sample by analyzing the released modified peptides using mass spectometry.