Patent ID: 6846679

Claim:
A method for characterising a populatin of parent polypeptides in a sample, which method comprises: (a) contacting a first portion of the sample with a first sequence-specific cleavage agent to generate polypeptide fragments; (b) isolating one or more polypeptide fragments, each fragment comprising the N-terminus or the C-terminus of the parent polypeptide from which it was fragmented; (c) identifying the isolated fragments by mass spectrometry; (d) repeating steps (a)-(c) on a second portion of the sample using a second sequence-specific cleavage agent that cleaves at a different site from the first cleavage agent, wherein the second cleavage agent is different from the first cleavage agent, and wherein the second portion of the sample is separate from the first portion of the sample; and (e) characterising the parent polypeptides in the sample from the fragments identified in steps (c) and (d).