Notes 2020.12.01

Comet’s terminal modification reporting

• Back in the early 2000s during the development of the pepXML format, reported n- and c-terminal modification masses would be reported with the addition of H and OH, respectively. This was based on a convention within my search code way back when.
• So an acetylated n-terminus (+42) would have its peptide string be reported as something like “n[43]DLASTK”.
• Similarly any c-terminal modification would be reported with an additional +17 mass.