Peptide tryptophan-derived

On hydrolysis with acids phalloidin yields L-alanine, 4-cis-L-hydroxyproline, D-threonine, L-y, -dihydroxyleucine, L-cysteine and j8-oxindolalanine ( oxytryptophan ). The tryptophan derivative is not a genuine building component of the cyclic peptides it is formed by hydrolysis of a thioether crosslink between position 2 of tryptophan and the side chain of cysteine (tryptathionine). The structure of the bicyclic heptapeptide is shown in Fig. 21. 

N-Terminal tryptophanyl peptide bonds are not cleaved by the action of NBS. The reason for the failure of the cleavage reaction may be related to the possibility that the free a-amino group of tryptophan derivatives and not the carboxamido function interact preferentially with the bromoindolenine. Similar amino group participation has been found with N-terminal tyrosyl peptides, which are not cleaved by NBS (434). 

Finally, the yellow color of the tryptophan derivatives is a convenient chromatographic marker for peptides (278). In particular, 2-nitro-4-carboxyphenylsulfenyl chloride has been used for identifying tryptophan pepjtides in the diagonal electrophoresis technique (253). 

Tryptophan and tryptophan-containing peptides and proteins specifically react in formic acid containing dry HCl to give the corresponding 1-formyl-tryptophan-derivative (186) (310). This modification can... 

Although the reaction of nitrous acid with peptides and proteins has been extensively used for analytical purposes (van Slyke estimation), the nature of the organic products has often been overlooked. Recently, Bonnett and Holleyhead 49) reported that treatment of N-acyl-tryptophan derivatives with sodium nitrite under mildly acidic conditions furnishes nitrosamines with the nitroso group located at the indolic nitrogen. 

The reaction takes place smoothly in about 50% yield in aqueous acetic acid at room temperature with simple tryptophan derivatives and also with tryptophan peptides. The N-nitrosamine bond in the tryptophan derivatives is cleaved by mineral acids, such as HBr in acetic acid. The derivatives are also photolabile, so that the electronic spectra cannot be measured accurately. 

In a recent study 321) the shifts and linewidths of aqueous solutions of amino acids, peptides, and derivatives have been correlated. It was seen that the groups directly bonded to the a-nitrogen atom determine the region in which the shift occurs, but other groups in the molecule, or intermolecular interactions, may cause small perturbations within that region. The extreme of the observed shifts in the oc-amino acids are 332 and 346 ppm (with trimethyl-phenyl-ammonium chloride chosen as external secondary standard). In the case of tryptophan at pH 7.15 the shift was observed at 343 ppm. 

Certain amino acids and their derivatives, although not found in proteins, nonetheless are biochemically important. A few of the more notable examples are shown in Figure 4.5. y-Aminobutyric acid, or GABA, is produced by the decarboxylation of glutamic acid and is a potent neurotransmitter. Histamine, which is synthesized by decarboxylation of histidine, and serotonin, which is derived from tryptophan, similarly function as neurotransmitters and regulators. /3-Alanine is found in nature in the peptides carnosine and anserine and is a component of pantothenic acid (a vitamin), which is a part of coenzyme A. Epinephrine (also known as adrenaline), derived from tyrosine, is an important hormone. Penicillamine is a constituent of the penicillin antibiotics. Ornithine, betaine, homocysteine, and homoserine are important metabolic intermediates. Citrulline is the immediate precursor of arginine. 

Kostic el al. discovered that Pd11 complexes, when attached to tryptophan residues, can rapidly cleave peptides in acetone solutions to which a stoichiometric amount of water is added, for hydrolysis.436 The indole tautomer in which a hydrogen has moved from the nitrogen to C(3) is named indolenine. Its palladium(II) complexes that are coordinated via the nitrogen atom have been characterized by X-ray crystallography and spectroscopic methods.451 Binuclear dimeric complexes between palladium(II) and indole-3-acetate involve cyclopalladation.452 Bidentate coordination to palladium(II) through the N(l) and the C(2) atoms occurs in binuclear complexes.453 Reactions of palladium(II) complexes with indole-3-acetamide and its derivatives produced new complexes of unusual structure. Various NMR, UV, IR, and mass spectral analyses have revealed bidentate coordination via the indole carbon C(3) and the amide oxygen.437... 

Fluorescence is not widely used as a general detection technique for polypeptides because only tyrosine and tryptophan residues possess native fluorescence. However, fluorescence can be used to detect the presence of these residues in peptides and to obtain information on their location in proteins. Fluorescence detectors are occasionally used in combination with postcolumn reaction systems to increase detection sensitivity for polypeptides. Fluorescamine, o-phthalaldehyde, and napthalenedialdehyde all react with primary amine groups to produce highly fluorescent derivatives.33,34 These reagents can be delivered by a secondary HPLC pump and mixed with the column effluent using a low-volume tee. The derivatization reaction is carried out in a packed bed or open-tube reactor. 

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