Peptide fragments, chemical modification

Dongre A.R., Jones J.L., Somogyi A., and Wysocki G.H. (1996), Influence of peptide composition, gas-phase basicity, and chemical modification on fragmentation efficiency evidence for the mobile proton model, J. Am. Soc. Mass Spectrom. 118, 8465-9374. 

Chemical modification of the peptides prior to PSD MS measurement was proposed to improve sequence identification [95], to facilitate peptide specific fragmentation and to suppress a part of the spectrum in order to simplify it. Pappin,... 

In order to identify the amino acid residues in the antigenic reactive sites, the following three approaches have so far been pursued in BSA (1) studies on the immunochemistry and conformation of chemical derivatives of BSA specifically modified at particular amino acid residues, (2) the isolation of immunochemically reactive fragments liberated by proteolytic digestion of the protein, and (3) studies of the effects of chemical modification of selected amino acid residues on the immunochemistry and conformation of these immunochemically reactive peptides. 

The X-ray structure of spinach Rubisco identifies 10 loop regions in the active-site (8). The major photolabeled peptide isolated by ion-exclusion and ion-exchange chromatography, and reverse phase HPLC corresponded to the Rubisco LSu tryptic peptide Val-42 to Arg-79 (Table 1), an active-site peptide (9). Two portions of the tryptic peptide Asp-95 to Lys-128, the peptide which comprises loop B in the crystal structure (8) were also recovered. Also recovered were two peptides (Table 1) which include residues in two other loop regions of the Rubisco active-site (8). The peptide Asp-202 to Arg-213 (loop 2 in ref. 8) is adjacent to the activator lysine (10). The peptide Gln-259 to His-267 is the N-terminal fragment of Gln-259 to Arg-285 the tryptic peptide which encompasses loop 4. Thus, all four of the photoaffinity labeled LSu peptides have been previously shown to be active-site peptides based on X-ray crystallography or chemical modification or by both techniques. 

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