N-terminal groups

For the elongation of the chain starting from 11 toward the N-terminal group, direct condensation of the activated p-nitrophenyl esters of such amino acids as N-protected L-cysteine, L-glutamic acid, glycine, L-leu-cine, L-proline, L-serine, L-tyrosine, andL-valine with 2-acetamido-3,4,6-... 

Experimental values for these molecules are based on a different N-terminal group, an asparagine-quinoline moiety replacing NHj-Ala-Ala in the compounds 2,4,5,8 and 9. 

Note. N is the molecular weight of the neutral N-terminal group, C is the molecular weight of the neutral C-terminal group, and M is the molecular weight of the neutral amino acid residues. In order to obtain m/z values for positive ions, add the appropriate number of protons to obtain the required charge and divide by the number of charges. 

Finally, in the pH range of 9—10, the slope of the pH profile was unit positive, indicating specific hydroxide ion catalysis. It is thus apparent that the unprotonated N-terminal group imparts more reactively to the... 

The initial reagent for detecting the N-terminal group is an aryl isothiocyanate. R O H R O H R"... 

The incorporation of metal ligands onto peptidic structures is an active area of research. These compounds can be used as molecular devices to control the formation of supramo-lecular peptidic architectures, to induce and stabilize secondary structures, and as sensing devices for the detection of certain metals. The metal ligand group can be linked to the side chain of an amino acid and incorporated into a peptide chain, or it can be incorporated as a C- or N-terminal group. The strategy used depends on the application targeted. 

All peptides and proteins, unless they are cyclic, contain the so-called N- and C-terminal residues a free a-amino group at one end and a free a-carboxyl group at the other. The identity of such groups may be determined by various chemical and enzymatic means. One of the first such methodologies utilized fluorodinitrobenzene (FDNB) for N-terminal group analysis ... 

By inspection, it is clear that at pH 9, the carboxyl and the N-terminal groups are deprotonated, whereas the amino and guanido groups are protonated, to give —2 and 2 charges for a net of 0. 

The coordinates of the N-terminal group are expressed in the same local coordinate system as the amino acid residue. As an example, the CH3CO—... 

Acid proteases are inactivated by active-site specific reagents, diazoacetylnorleucine ethyl ester and other diazo compounds, and epoxy (p-nitrophenoxy)propane. Covalently labelled aspartic acid peptides have been isolated from pepsin, chymosin (= rennin), and penicillopepsin. The peptides labelled with the diazo compounds have similar sequences and differ from the epoxy (p-nitrophenoxy)pro-pane labelled peptides. These results indicate two aspartic acids at the active site and suggest homology between the enzymes. The latter is confirmed by a comparison of the sequence data. Studies of the action of porcine pepsin and penicillopepsin on some dipeptides with free N-terminal groups show transpeptidation involving a covalent acyl intermediate. It is proposed that there are differences in the mechanism of action of pepsin which are determined by the nature of the substrate. 

Although at least seven different amino acids are represented among the N-terminal groups and also among the C-terminal groups detected in... 

The presence of many different C- and N-terminal groups in low concentration in wool protein preparations may be due to the presence of many protein components, the rupture of different peptide bonds in a small number of different protein molecular species, the adsorption of amino acids or peptides on the proteins, or a combination of these possibilities. 

Middlebrook (1951) established that wool contains at least seven different N-terminal residues those of alanine, aspartic acid, glutamic acid, glycine, serine, threonine, and valine, but they were not present in simple molecular proportions (Table XVII). More recently, Thompson (1959) found that half-cystine is also an N-terminal residue and is the second most abundant. The most recent quantitative data relating to N-terminal groups in worsted fabric (Zahn et al., 1963) are similar to the results of Steuerle and Hille (1959) for Merino top wool (Table XVII). 

Summarizing, it would appear that wool contains both N-acetyl and a variety of amino N-terminal groups, and these latter are not entirely artifact in origin. The comparative paucity of terminal carboxyl groups... 

In the analysis for the N-terminal group in chain B of insulin, equal amounts of two different DNP derivatives of single amino acids actually were found. One was DNP.Phe what could the other have been ... 

Hepworth and coworkers95 have studied the effects of iV-alkyl and heterocycloalkyl substituents on the light absorption properties of, Victoria Blue 35 and 36 (Figure 12), the 1-naphthyl analogue of Crystal Violet. The steric interaction found between the N-terminal group and the peri-hydrogen in the naphthyl residue is correlated with H NMR data. 

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