E-Amino groups

At pH 4-5, the reaction is selective for protection of thiol groups in the presence of oc- or e-amino groups. 

Benzylsulfonamides, prepared in 40-70% yield, are cleaved by reduction (Na, NH3, 75% yield H2, Raney Ni, 65-85% yield, but not by H2, Pt02) and by acid hydrolysis (HBr or HI, slow). They are also cleaved by photolysis (2-4 h, 40-90% yield). The similar p-methylbenzylsulfonamide (PMS—NR2) has been prepared to protect the e-amino group in lysine it is quantitatively cleaved by anhydrous hydrogen fluoride/anisole (—20°, 60 min). Another example of this seldom used group is illustrated below... 

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

FIGURE 6.1 All electrostatic interaction between the e-amino group of a lysine and the 7-carboxyl group of a glutamate residue. 

FIGURE 18.32 Biotin is covalently linked to a protein via the e-amino group of a lysine residue. The biotin ring is thus tethered to the protein by a 10-atom chain. It functions by carrying carboxyl groups between distant sites on biotin-dependent enzymes. 

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. 

Histone Acetylation. Figure 1 Histone acetylation is a posttranslational modification of lysine residues of histones. This modification is catalyzed by histone actyl transferases (HATs), which transfer an acetyl group (yellow) from acetyl-Coenzyme A onto the E-amino group of the lysine residue. Histone deacetylation is catalyzed by histone deacetylases (HDACs), which hydrolyze the lysine bound acetyl group. HDAC inhibitors like Trichostatin A (TSA) are known to inhibit the deacetylation reaction in vivo and in vitro. 

On the whole, curing procedures appear a promising way to obtain very stable polymer films. Thus, the structure of already mentioned polylysine has been revised as a block polymer involving either the a or e amino groups of lysine Vitamin Bj2 modified carbon electrodes were prepared by thermal curing of a mixture of a diamino functionalized derivative 5 and an epoxy prepolymer 6 of the araldite... 

Figure29-1. Partial reactions in the attachment of ubiquitin (UB) to proteins. (1) The terminal COOH of ubiquitin forms a thioester bond with an -SH of E, in a reaction driven by conversion of ATP to AMP and PP. Subsequent hydrolysis of PP by pyrophosphatase ensures that reaction 1 will proceed readily. (2) A thioester exchange reaction transfers activated ubiquitin to Ej. (3) E3 catalyzes transfer of ubiquitin to e-amino groups of lysyl residues of target proteins.

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). 

Another interesting target for this type of inhibitors is the dipeptidyl peptidase IV (DPP IV). This exodipeptidase, which can cleave peptides behind a proline residue is important in type 2 diabetes as it truncates the glucagon-like peptide 1. Taking into account the P2-Pi( Pro)-P,1 cleavage and the requirement for a free terminal amine, the synthesis of a suicide inhibitor was planned. It looked as if the the e-amino group of a P2 lysine residue could be cyclized because of the relative little importance of the nature of the P2 residue on the rate of enzymatic hydrolysis of known synthetic substrates. Therefore, anew series of cyclopeptides 11 was synthesized (Fig. 11.8). 

N-donor groups in the form of e-amino groups of lysine as nonspecific binding sites for technetium may play an undesired role in Tc-labelling of monoclonal antibodies for tumour imaging [51]. Nonspecifically bound Tc has a poor in vivo stability and appears to increase the undesired liver uptake and reduces tumour uptake. The metal oxidation state and coordination is not yet known. 

The transglutaminases are calcium-dependent enzymes that catalyse the cross-linking of proteins by promoting the formation of isopeptide bonds between the /-carboxyl group of a glutamine in one polypeptide chain and the e-amino group of a lysine in the second (Greenberg et al., 1991). These... 

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. 

Proteins may be modified with oxidized dextran polymers under mild conditions using sodium cyanoborohydride as the reducing agent. The reaction proceeds primarily through e-amino groups of lysine located at the surface of the protein molecules. The optimal pH for the reductive amination reaction is an alkaline environment between pH 7 and 10. The rate of reaction is greatest at pH 8-9 (Kobayashi and Ichishima, 1991), reflecting the efficiency of Schiff base formation at this pH. 

Sashidhar, R.B., Capoor, A.K., and Ramana, P. (1994) Quantitation of e-amino group using amino acids as reference standards by trinitrobenzene sulfonic acid./. Immunol. Meth. 167, 121-127. 

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]. 

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