Patent ID: 7501286
Filing Date: 2009-03-10
Classification: G01N,Y10T

Abstract:
1. A method for determining the presence and/or quantity of a modified target polypeptide in at least one mixture of different polypeptides, comprising: a) providing a mixture of different polypeptides; b) adding a known quantity of a single peptide internal standard labeled with a mass-altering label, thereby generating a spiked mixture, wherein the labeled peptide internal standard comprises a subsequence of the target polypeptide and wherein the labeled peptide internal standard possesses a known peptide fragment signature diagnostic of the presence of the peptide; c) treating the spiked mixture with a protease activity to generate a plurality of peptides including the labeled peptide internal standard and peptides corresponding to the target polypeptide; d) fragmenting the labeled peptide internal standard and any target peptide present in the spiked mixture comprising the same amino acid sequence as the labeled peptide internal standard; e) determining the ratio of labeled fragments to unlabeled fragments; and f) calculating from the ratio and the known quantity of the labeled internal standard, the quantity of the target polypeptide in the mixture.