Tryptophan modification

Ohmiya, Y., Ohashi, M., and Tsuji, F. I. (1992). Two excited states in aequorin bioluminescence induced by tryptophan modification. FEBS Lett. 301 197-201. 

Previero, A., A. Signor, and S. Bezzi. Tryptophan modification in polypeptide chains. Nature 204 687-688, 1964. 

Modification of Tryptophan Residues. Tryptophan residue also could be determined quantitatively by a modification with a sulfenylating agent such as 2-nitrophenyl sulfenyl chloride in 30% acetic acid ( ). Since both oxidized and sulfenylated tryptophan gave characteristic absorption at 365 nm, the extent of tryptophan modification was calculated from the mean difference between the sulfenylated protein and the kynurenine. The absorption contributed by kynurenine was comparatively weak. 

Tryptophan modification, peptide-bond cleavage derived from skatole, which is also known as boar taint. 

Antos JM, Francis MB. Selective tryptophan modification with... 

Antos JM, Francis MB. Selective tryptophan modification with rhodium carbenoids in aqueous solution. J. Am. Chem. Soc. 2004 126 10256-10257. 

Fig. 10.3-9 Tryptophan modification using addition to reacting with the aqueous rhodium carbenoids. (a) These species can solvent. Control experiments that were run be formed in situ through the reaction of in the absence of rhodium catalyst afford no...

Figure 8. Effect of tryptophan modification by NBB (2-hydroxy-5-nitrobenzylbromide) on anticomplementary activity of rabbit IgG and its Fc fragment. IgG was first modified and then heat-aggregated. Modified Fc was tested as such. Results refer to 100 /i,g of each preparation. Reproduced with permission from Allan and Isliker (1974a) copyright 1974, Peigamon Press, Ltd.

The modification of tryptophan in proteins has been shown by a number of authors using various modifying agents. In our studies on the tryptophan modification of TK, we have used dimethyl-(2-hydroxy-5-nitrobenzyl)-sulfonium chloride, recently introduced by Horton and Tucker. These authors have shown that the degree of labelling of proteins by HNB depends on the reagent to protein ratio and on the pH of the reaction mixture [14]. 

Recently, Francis etal. reported the selective modification of tryptophan indole side chains in several proteins with a diazo reagent catalyzed by dirhodium tetraacetate [44], and Ball etal. achieved remarkable rate accelerations for tryptophan modification (>10 ) using dirhodium metallopeptides (Section 9.3.2) [45]. 

Bachmayer, H., 1972, Effect of tryptophan modification on the activity of bacterial and viral neuraminidases, FEBS Lett. 23 217-219. 

In this present investigation, tryptophan residues on the CCBE and CNBE molecule were modified with NBS to assess the role of these residues in catalytic/substrate binding.The results of tryptophan modification by NBS showed that one Trp residue existed in the active site of CCBE s chitosanolytic activity,while two were involved in the active site of its CMCase one located in the substrate binding domain,and the other located in the catalytic domain. Modification of enough Trp residues will lead to the completely loss in both activities of CCBE, suggesting that the tryptophan also help for the stability of enzyme conformation. 

In the following, the most frequently used reagents for tryptophan modification are discussed, while the effects of modifications on biological properties of enzymes are presented in Section VII. 

Sulfenyl halides possess several particularly valuable features for protein modification studies. Their high selectively for tryptophan in proteins lacking SH-groups is especially remarkable. Furthermore, even if cysteine residues are present, selectivity for tryptophan can still be achieved since the disulphides formed by reaction of the halide with cysteine SH-groups can be easily reconverted to cysteine by subsequent reduction with mercaptoethanol. Other techniques for tryptophan modification are less specific and in several cases the reaction products are undefined. 

CuATRECASAS et al. (92) observed that TNM can cause nitration of the single tryptophan residue in staphylococcal nuclease, but the nature of the nitro derivative was not determined. The inactivation of papain by TNM has also been thought to be due to tryptophan modification 264). Nitration has been observed also with lactoferritin 407). 

Several studies of proteins have been made on the assumption that specific reactions occur between the reagents used and the tryptophan residues in proteins. This ideal condition is rarely fulfilled. It is worth recalling that, although extensively used for tryptophan modification studies, NBS is by no means selective for the indole nucleus of tryptophan and also the final modification products cannot be defined unambiguously (438). A similar situation is also presented by the Koshland reagent, which was shown to give, upon reaction with model tryptophanyl compounds, up to ten different products (168, 236, 253, 378). 

Bachmayer, H. Effect of Tryptophan Modification on the Activity of Bacterial and Viral Neuramidase. FEBS Lett. 23, 217-219 (1972). 

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