Practice question

Lysine residues undergo enzymatic acetylation where an acetyl group CH3CO replaces hydrogen on epsilon amino group, neutralizing positive charge and regulating chromatin structure and metabolism. Addition of C2H2O minus H corresponds to monoisotopic mass increment of 42.0106 Da, observed as +42 Da shift in mass spectra. Detecting this modification on peptides helps identify epigenetic regulatory marks and metabolic regulation. Differentiation from trimethylation which also adds ~42 Da requires high resolution or diagnostic fragment ions, but in typical low-resolution proteomics workflows +42 Da strongly suggests acetylation event on proteins.