FIGURE 4.

Mass spectra of a dipeptide produced by mouse ATPGD1. Homogenous recombinant mouse ATPGD1 was incubated for 18 h with 3 mm β-alanine and 3 mm l-histidine in the absence or presence of 3 mm MgATP. The produced dipeptide was purified and submitted to mass spectrometry either as such or after acetylation with acetic anhydride. Tandem mass spectra of the putative carnosine (A) and N-acetylated carnosine (B) were acquired. The identity of the carnosine fragment ion at m/z 180 was [M + H − H₂O − HCO]⁺.