FIGURE 1.

ESI-MS/MS analysis of the glycopeptide produced in the P. calidifontis membrane fractions. The Triton X-100-solubilized membrane fractions of the P. calidifontis cells were incubated with an acceptor peptide, Ac-AAYNVTKRK(TAMRA)-OH. The purified glycopeptide product was analyzed by direct infusion ESI-MS/MS, in the positive ion mode. The triply charged monoisotopic precursor ion is marked by the vertical arrow. The inset shows the predicted chemical structure of the glycopeptide and the MS/MS fragmentation scheme. The branching structure of the N-glycan was determined by NMR analysis (unpublished data). The expected m/z values were observed within 0.02 of the theoretical mass values for triply charged fragment ions.