MALDI-TOF mass spectrum of large peptide fragments produced by SSO0551 partial trypsin proteolysis. A partial enzymatic proteolysis was carried out during 60 sec at 20°C with a trypsin/SSO0551 protein ratio of 1/20 (w/w). The products were then resolved onto a C8 reverse phase chromatographic column and the different UV absorbing fractions were analyzed by MALDI-TOF. The m/z spectrum obtained with the fraction eluting at 40–50 % acetonitrile is shown. The asterisk labels a peak arising from trypsin autolysis. Peaks that could be assigned are identified with numbers (experimental m/z, residues, Δmass in ppm compared to theoretical [M+H]+ average mass): M1 (19198.4, [1–166], -1), M2 (15478.7, [32–166], -53), M3 (15191.2, [35–166], +153), M4 (12883.4, [52–162] or [56–166], -46 or -43), M5 (12724.2, [57–166], +193), M6 (10603.8, [76–166], +51), M7 (10220.1, [79–166], +77), M8 (9257.2, [83–162], +63) and M9 (7717.0, [101–166], -134). Peptides C1 and C2, complementary of M5 and M6, were not observed in this spectrum but in another fraction from the C8 reverse-phase chromatography corresponding to smaller peptides.