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. 2002 Mar;184(5):1234–1243. doi: 10.1128/JB.184.5.1234-1243.2002

FIG. 6.

FIG. 6.

ESI-FTICR-MS analysis of the reaction products formed by MrsD. The substrate peptides MrsA and His-MrsA, respectively, were incubated with MrsD, and the reaction mixtures were then analyzed by RPC. Reaction product containing fractions characterized by an increased absorbance at 260 nm (compare Fig. 5) were analyzed by ESI-FTICR-MS, and the obtained spectra were compared with the spectra of the substrate peptides. (A) The mass difference between MrsA and the reaction product is 46.0009 Da. (B) The mass difference between His-MrsA and the reaction product is 46.0023 Da. For calculation of the mass differences, only m/z values of the 5-fold charged ions (MrsA) and the 10-fold charged ions (His-MrsA; peaks with the highest intensity), respectively, were used. The observed mass differences are explained by oxidative decarboxylation of the COOH-terminal cysteine residue of the substrate peptides. The monoisotopic mass of “H2CO2” is 46.0055 Da (used atomic masses [in atomic mass units]: C, 12.00000000; H, 1.00782504; and O, 15.9949146).