The e-Amino Group of Lysine

The side-chain amino group of lysine is a strong nucleophile, the reactivity of which cannot be suppressed by protonation, so it must be protected at all times. Acyl groups such as formyl, which is stable to alkali, ammonia, and hydrogenation but sensitive to mild acid, and trifluoroacetyl (see Section 3.9), which is stable to piperidine and 

A Aletras, K Barlos, D Gatos, S Koutsogianni, P Mamos. Preparation of very acid-sensitive Fmoc-Lys(Mtt)-OH. Int J Pept Prot Res 45, 488, 1995. 

E Atherton, V Wooley, RC Sheppard. Internal association in solid phase peptide synthesis. Synthesis of cytochrome C residues 66-104 on polyamide supports, (trif-luoroacetyl) J Chem Soc Chem Commun 970, 1980. 

BW Bycroft, WC Chan, SR Chhabra, ND Hone. A novel lysine-protecting procedure for continous flow solid phase synthesis of branched peptides. (Dde group) J Chem Soc Chem Commun 778, 1993. 

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Calculate the pH at which the e-amino group of lysine is 20% dissociated. 

Histone acetylation is a reversible and covalent modification of histone proteins introduced at the e-amino groups of lysine residues. Histones and DNA form a complex - chromatin - which condenses DNA and controls gene activity. Current models interpret histone acetylation as a means to regulate chromatin activity. 

Transamination is not restricted to a-amino groups. The 5-amino group of ornithine—but not the e-amino group of lysine—readily undergoes transamination. Serum levels of aminotransferases are elevated in some disease states (see Figure 7-11). 

Add a quantity of the appropriate isobaric tag solution to each sample to provide a final concentration of 10-20 mM. This quantity of reagent will assure a large molar excess of reagent over the concentration of peptides present in order to modify completely all peptides at their N-terminus. Note that the e-amino groups of lysine residues also will be modified by this procedure. React for 1 hour at room temperature. 

It should be noted that the majority of the derivatization techniques modify the peptide s N-terminus. The reason is that the N-terminal amine group is easier to modify than the C-terminal carboxyl group. Also, due to differences in pKa value in the e-amino group of lysine, there are possible reaction that modify the N-terminus only, while the lysine side chains remain intact. Modifications of carboxyl groups... 

Silk fibroin contains no cystine and the content of lysine and histidine is also low (about 1% in total), but it does contain tyrosine phenolic (13%) and serine alcoholic (16%) sidechains. Since glycine accounts for 44% of the total aminoacid content, an N-terminal glycine residue is reasonably representative of most of the primary amino dyeing sites in silk fibres. Amino acid analysis of hydrolysed reactive-dyed silk indicates that the reaction between fibroin and reactive dyes takes place mainly at the e-amino group of lysine, the imino group of histidine and the N-terminal amino group of the peptide chain. In an alkaline medium, the hydroxy groups of tyrosine and serine also react [114]. 

Penicillins and cephalosporins bind irreversibly to serum albumin. It has been shown that drug-protein conjugates result from the aminolysis of the /3-lactam bond by the e-amino group of lysine residues in the protein (Fig. 5.1, Pathway e). The bound penicilloyl group appears to be the major antigenic determinant of penicillin allergy [145-148],... 

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