FIG.2.

Identification of EppA by mass spectrometry. (A) MALDI-TOF spectrum of EppA protein. The spot corresponding to phosphorylated EppA was excised and digested with trypsin. The tryptic peptides were extracted and subjected to MALDI-TOF analysis. Peaks that match theoretical tryptic digested peptide masses from EppA are marked by asterisks. (B) Amino acid sequence of EppA. The amino acid sequence was derived from full-length cDNA sequences (clone sVFD141 and AFK 496) provided by the Japanese Dictyostelium cDNA project. Four potential Erk2 phosphorylation sites (Ser/Pro) are labeled with asterisks. Amino acids sequenced by LC-MS/MS are boldfaced, and sequences covered by MALDI-TOF are underlined. (C) Mass spectrum of potential phosphopeptide. A portion of panel 2A was enlarged to show a peak (1,244.45 Da) (left arrow) potentially representing the peptide containing serine 250 (amino acids 245 to 255) and the peak (1,323.42 Da) (right arrow) potentially representing the phosphorylated peptide.