Figure 2.

(A) Sequence of PKA showing the 42 identified peptides that were observed in a single MALDI-TOF mass spectrum. The peptides cover 65% of the PKA sequence including two of the phosphorylation sites, which were identified as phosphopeptides in the mass spectrum. (B) Sequence of human thrombin showing the 29 identified peptides that were observed in a single MALDI-TOF mass spectrum. The sequence is numbered sequentially, although in the text the chymotrypsin-numbering system notation is given as well. The peptides cover 50% of the thrombin sequence. The cysteines that form the disulfide bonds between C9 and C155, between C64 and C80, between C209 and C223, and between C237 and C267 are shown in bold letters. The disulfide bonds were not reduced, and coverage of the sequence near the disulfide bonds appears to be inefficient.