isotope tagged reagent derivatized residue isotope tagged reagent acylated residue iTRAQ4plex reporter+balance reagent N-acylated residue iTRAQ4plex reporter+balance reagent acylated residue, average mass modification (4-methylpiperazin-1-yl)acetyl 144.100006103515625 144.1024169921875 A protein modification that effectively replaces a hydrogen atom of a residue with one of the Applied Biosystems iTRAQ4plex reagent reporter+balance groups. MOD:02028 PSI-MOD The reagent consists of a reporter group, a balance group and a protein reactive N-oxysuccinimide group. The reporter group, an isotopically labeled 1,4-dimethylpiperazine, is connected to a carbonyl balance group that is isotopically labeled to produce a nominally isobaric combined modification. Four versions of chemically identical iTRAQ4plex moyeties, but with different isotope distribution. This modification is calculated as the average of the four species. It has no isotopic distribution reality, the exact mass does not correspond to any real isotopic distribution. X artifact iTRAQ