Fig. 2. Mass spectrometric analysis of a tryptic digest obtained from the ADP-ribosylated ∼53 kDa mitochondrial protein. The incubation and separation of the modified protein were conducted as described in the legend to Figure 1. Following SDS–PAGE, the protein band containing the radioactive label was subjected to ‘in-gel’ digestion with trypsin. The mass spectrum of the resulting peptides was obtained by MALDI-TOF spectrometry. Only masses corresponding to internal peptides of GDH are indicated, assuming a maximum of one missed cleavage site per peptide. The asterisks indicate peaks corresponding to GDH peptide masses, considering more than one missed cleavage site or oxidized methionine residues.