FIGURE 7.
MALDI-TOF mass spectra of DEPC modification of the synthetic His-rich decapeptide before (A) and after (B) Cu2+ incubation. Integers over the peaks represent the calculated number of carbethoxylations. Note that all eight of the His residues and two other functionalities appear to be monocarbethoxylated DEPC (A, i), which prevents any Cu2+ binding that can be detected by MALDI-TOF (A, ii). Conversely, Cu2+ binding prior to DEPC exposure abolishes monocarbethoxylation by any peptide functionality (B, i and ii).