[2] TAILS is a 2D or 3D proteomics based assay for the labeling and isolation of N-terminal peptides, developed by a group at the University of British Columbia.
[2] Samples can be derived from a variety of sources including tissue, fibroblasts, cancer cells and from fluid effusions.
The types of TAILS differ in the methods used to block and label the amino groups of the proteins and protease cleavage products.
[1] Stable isotope labeling with amino acids in cell culture (SILAC) is a procedure that can be done in vivo.
This metabolic labeling enables inhibition of a given protease in biological samples and analysis of ex vivo processing.
This method has the ability to simultaneously analyze from 4-8 samples in multiplex experiments using four- and eight- plex iTRAQ reagents.
The down side to this method is that the findings cannot be applied to a statistical model using non-cleaved peptides due to not being able to capture naturally blocked N-termini.
[4] Subtiligase biotinylation of N-termini uses enzymatic labeling of N-terminal peptides, but does not use lysine blocking chemicals.
This method does not capture naturally blocked N-termini and also does not use isotopic labeling thus it would be difficult to quantify findings.
The down side to this technique is that MALDI mass spectrometer is needed and the iTRAQ reagents required are costly.
[6] Combined fractional diagonal chromatography (COFRADIC) allows different labeling for naturally blocked N-termini and protease generated neo-N-termini.
The best separation results are dependent on the amino acid modification such as methionine oxidation not occurring during handling.