Peptidomics endogenous peptides

Nearly all of the published SILAC studies have been for studies on prote-omics, although it is technically possible to use this technique for studies on endogenous peptides. One peptidomic study used SILAC to investigate the production of peptide hormones in cell culture (50). 

Being a relatively rare residue, labeling of cysteines by ICAT reduces complexity in the sample mixture (51), making it a convenient methodology for proteomics. The same property makes it inefficient for peptidomic analyses, since most endogenous peptides do not contain cysteine residues. 

There are several examples of peptidomic studies using iTRAQ labeling. One study identified substrates of prolyl peptidases in mouse models, and another explored the effect of diurnal variation on the endogenous peptide composition of human parotid saliva (64,65). 

Proteolytic labeling has not yet been applied to peptidomic analysis, which is carried out in the absence of enzyme digestion. However, sample preparation under lsO-enriched conditions, allowing for the endogenous peptide pool... 

---