Is it really acetylated and where you think? Check the chromatography!

 

Acetylations can occur on multiple amino acids in your peptides and it's no secret that most search tools struggle with localization of modification sites (that's why we have A-score and ptmRS to help).

This group looked at loads of modified and acetylated peptides in terms of how they elute on reverse phase and other types of chromatography. 

If you're really stuck on that site and whether it's: A) real and B) where it is located, this might help?