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Unknown peptide modification in the Peptide standard

Question asked by bastibergdahl on Oct 22, 2018

Hi all,

We have started using the Ten-peptide standard, 71 µg, lyophilized, in a 2 mL vial ( ) as a quality control sample in our LC-MS/MS analysis runs. We are using MSGF in OpenMS to identify the peptides and are able to find all except peptide number 7:

[Ace-F-3,-2 H-1] Angiotensinogen (1-14) Ace-FFHDRVYIHPFHLLVYS.


According to the Certificate of Analysis ( ) the molecular weight of this peptide is 2231.61 Da. However, a check in the NIST Mass and Fragment Calculator v1.3 the monoistopic mass of the acetylated peptide is 2231.13 Da

I would be very grateful if someone could explain to me what other modifications are made to this peptide and how I can specify it in a search engine such as MSGF.

Thank you in advance!