Figure 1
From: Precise protein quantification based on peptide quantification using iTRAQ™
Chemical structure of the iTRAQ™ reagent. The label is composed of a peptide reactive group (red, NHS ester) and an isobaric tag of 145 Da, which consists of a balancer group (blue, carbonyl group) and a reporter group (green, N-methylpiperazine). The four available tags of identical overall mass vary in their stable isotope compositions such that the reporter group has a mass of 114–117 Da and the balancer of 28–31 Da. The fragmentation site between the balancer and the reporter group is responsible for the generation of the reporter ions in the region of 114–117 m/z.