Peptides, derivatization specificity

J.A. Shin, Specific DNA binding peptide-derivatized solid support, Bioorg. Med. Chem. Lett. 1997, 7,2367. 

The peptide mixture on the MALDI target can be exposed to a chemical derivatization to confirm the identity of a peptide by the mass shift associated with the sequence-specific derivatization. A large number of possible derivatization reactions can be combined with the MALDI-TOF analysis. Their usefulness depends critically on the kinetics of the derivatization reaction, whether the reaction is complete with small amounts of peptides and whether only one product is generated. A visible MALDI signal can be generated from low atomole of peptide present under the laser beam (Vorm et al., 1994), but these amounts are often not sufficient... 

Disulfide connectivities of a partially reduced and alkylated peptide can be identified by the pairwise recognition of the specifically derivatized PTH-Cys on sequencing/46 PTH-Cys(Cam) and PTH-Cys(CM) are reported to elute on the ABI sequencer with PTH-Glu and PTH-Ser, respectively/46 and PTH-Cys(NEM) after PTH-Pro. 49 Therefore, it is important to know the primary structure of the target molecule in advance and to focus on the determination of its disulfide arrangement during sequence analysis in order to avoid mis-assignment of the amino adds at the cycles of the modified cysteine residues. 

Colistin is a linear-ring peptide antibiotic. Its main components are colistin A and colistin B. It is a member of the polymyxin family of antibiotics that is stable in dry form and in water solution. The sulfate salt of colistin, which is usually administered as feed additive, is soluble in water, slightly soluble in methanol, and practically insoluble in acetone and ether. Colistin components do not have any specific fluorophore and UV chromophore, so detection by liquid chromatography at residue levels of interest is difficult without including a suitable derivatization step in the analytical method. 

The specific peptide composition can be used to characterize foods. Abe (124) separated the peptides carnosine, anserine, and balenine from the white and red muscle of nine species of marine fishes. Carnegie et al. (37,38) developed an HPLC method using a Partisil-lOSCX column with 0.2 M lithium formate at a pH of 2.9 and a temperature of 40°C under isocratic conditions with postcolumn derivatization using OPA to separate the dipeptides of histidine, anserine, carnosine, and balenine from the muscles of various species (pork, chicken, beef, lamb, and mutton) in order to identify the origin of the meat used in meat products. The concentration of balenine and the balenineranserine ratio were higher in pork than in the other meats, and these relationships were useful in determining the presence of pork in mixtures with other meats. 

Peptides are commonly detected by absorbance at 200-220 nm. However, most of the compounds present in wine may interfere in the ultraviolet detection of peptides when low wavelengths are used. Thus, for the analysis of these compounds it is useful to apply sensitive and selective detection methods. To this end, it is possible to form derivates of the peptides that can be detected at higher and more specific wavelengths. Detection by fluorescence can also be used to detect peptides containing fluorescence amino acids (tyrosine and tryptophan). For peptides without this property, the formation of derivates with derivatizing agents have been proved to be very useful (Moreno-Arribas et al. 1998a). 

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