Post translational modifications, understood as covalent attachment of chemical moiety to protein molecule, can be identified and localized by mass spectrometry. The most ubiquitous PTMs are: phosphorylation, glycosylation, methylation, acetylation, ubiquitination etc. Sample preparation for PTM analysis generally resembles the standard procedure for protein identification, during which protein is degraded to peptides by proteolytic enzyme and resulting peptides are separated on HPLC and measured on a mass spectrometer. Conversion of a peptide into peptide ion is a critical moment in the measurement and this process depends on various factors, including peptides' amino acid sequences. This is the reason why we usually can't observe all peptides originating from the protein of interest.

Compared to protein identification, PTM analysis is more complicated. A protein can be reliably identified on the basis of a single peptide. However, when looking for a modification, we have to observe the exact peptide carrying the modification. To improve protein coverage, the sample for PTM analysis should be as pure as possible and provided in a substantial amount. Frequently, different enrichment methods have to be applied, or protein isolation protocol has to be modified to increase the probability of PTM identification. For this reason, we are asking you to contact our staff and discuss all the details concerning the analysis before any samples are sent to us.