derives from 1'-phospho-L-histidine phosphohistidine immonium ion 1'-phosphohistidine immonium ion -26.987638473510742188 -27.0 1+ 190.03759765625 190.1199951171875 2-((1-phosphono-1H-imidazol-4-yl)ethaniminium A protein modification that effectively converts an N-terminal 1'-phosphohistidine residue to 1'-phosphohistidine immonium ion. C -1 H 1 N 0 O -1 C 5 H 9 N 3 O 3 P 1 MOD:00044 MOD:01797 Ntau-phosphorylated L-histidine PSI-MOD This fragment corresponds to the first ion in an a+ series. artifact