MALDI-TOF and Peptide Fingerprints

Compare MS ions with those of a theoretical tryptic digest of alt candidate proteins in database for the best match -and identification (ID). 

Peptide Mixture ionized directly for MS/MS by ESI or Mixture Mixture separated by LC ionized for MS/MS  

Modification Amino Acid Average Mass Change 

Common posttranslational modifications of proteins. Frequently modified amino adds for each moiety are described. Most modifications involve low-mass substituents ( 500amu), but some modifications are small polypeptides of considerable mass such as ubiquitin or highly related peptide isomers like SUMO-1, SUMO-2, and SUMO 3. SUMO is the abbreviation for similar to ubiquitin methyl organizer , SUMO has different family members (SUMO 1, 2, and 3 that can combine with proteins). 

It is important to note that each of these ionization sources, either a laser in MALDI-TOF or the high voltage ionization of droplets in ESI-MS/MS or LC-MS/ MS, will each produce a different spectrum of detectable ions and intensities because the effectiveness and nature of peptide ionization is quite different for each source. In addition, the presence of multiple peptides that influence each other s ionization potential notably through ion suppression makes most peptide ion measurements only semiquantitative. 

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