derives from 1'-phospho-L-histidine phosphohistidine immonium ion 1'-phosphohistidine immonium ion -26.987089157104492188 -27.0 190.03814697265625 190.1199951171875 2-((1-phosphono-1H-imidazol-4-yl)ethaniminium This fragment corresponds to the first ion in an a+ series. none Ntau-phosphorylated L-histidine MOD:01797 C 5 H 9 N 3 O 3 P 1 MOD:00044 PSI-MOD C -1 H 1 O -1 A protein modification that effectively converts an N-terminal 1'-phosphohistidine residue to 1'-phosphohistidine immonium ion. artifact 1+