Peptides MALDI-QITs

Fig. 5. Representative peptide mass fingerprint for the 33.2 and 66.6 kDa proteins resulting from an in-gel digestion of the 66.6 kDa gel band obtained by MALDI-TOF mass spectrometry. Peptides marked with an asterisk result from autodigestion products of recombinant trypsin. Peptides labeled with a diamond were selected for MS/MS experiments carried out on a MALDI-QIT/RTOF and a nano-ESI-QIT mass spectrometer.

Fig. 6. (A) Low-energy CID spectrum (obtained by means of a nano-ESI-QIT instrument) of the doubly charged precursor ion (m/z 859.07) of the peptide with the amino acid sequence lANNVQPILTSrV. (B) Low-energy CID spectrum (obtained by means of a MALDI-QIT/RTOF instrument) of the singly charged precursor ion (m/z 1717.15) of the above-mentioned peptide.

Summary of the 12 peptides and their amino acid sequences revealed after MS/MS experiments obtained either on a MALDI-QfT/RTOF or on an off-hne nano-ESl-QIT mass spectrometer... 

The peptide at m/z 1717.15 is moreover a very good example to illustrate the fact that both techniques (MALDI and ESI) and instruments (QIT/RTOF and QIT) complement each other to corroborate and supplement the results (Fig. 6). After interpretation of the MALDI CID spectra sequence, uncertainties due to too many possible dipeptide masses in the low mass range existed. However, missing information on parts of the sequence elucidated from the nano-ESI CID spectrum could be unequivocally reassigned after taking the information from the MALDI MS/MS spectra into account. 

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