Tryptophan radical

Ru(dppz)(x) (y)3+/ Me, tryptophan AG -0.6 V detect G(-H), M, and tryptophan radical s by transient absorption, EPR Gs in intervening sequence k 107 s 1 up to 50 A CT not rate limiting up to 50 A GGox varies with sequence, base-stack pertubrations and extent of intercalation... 

For tryptophan, there seems to be an equilibrium, which could also lead to some tryptophan radical formation and subsequent protein damage ... 

Jensen, G. M., D. B. Goodlin, and S. W. Bunte. 1996. Density Functional and MP2 Calculations of Spin Densities of Oxidized 3-Methylindole Models for Tryptophan Radicals. J. Phys. Chem. 100, 954. 

Jin F, Leitich J, von Sonntag C (1993) The superoxide radical reacts with tyrosine-derived phenoxyl radicals by addition rather than by electron transfer. J Chem Soc Perkin Trans 2 1583-1588 Jonsson M, Lind J, Reitberger T, Eriksen TE, Merenyi G (1993) Free radical combination reactions involving phenoxyl radicals. J Phys Chem 97 8229-8233 Jovanovic SV, Simic MG (1985) Repair of tryptophan radicals by antioxidants. J Free Rad Biol Med 1 125-129... 

Deeble DJ, Schuchmann MN, Steenken S, von Sonntag C (1990) Direct evidence for the formation of thymine radical cations from the reaction of SO/" with thymine derivatives a pulse radiolysis study with optical and conductance detection. J Phys Chem 94 8186-8192 DeFelippis MR, Murthy CP, Faraggi M, Klapper MH (1989) Pulse radiolytic measurement of redox potentials the tyrosine and tryptophan radicals. Biochemistry 28 4847-4853 Delatour T, Douki T, D Ham C, Cadet J (1998) Photosensitization of thymine nucleobase by benzo-phenone through energy transfer, hydrogen abstraction and one-electron oxidation. J Photo-chem Photobiol 44 191-198... 

Fig. 3.6 Solvent access surfaces (colors represent electrostatic potentials) showing the exposed tryptophan residue (as yellow van der Waals spheres) involved in oxidation of lignin and other high redox-potential substrates by VP (a) and LiP (b). Lignin can be directly oxidized by VP at the tryptophan radical, while LiP requires the simultaneous presence of VA (synthesized by the fungus) acting as an enzyme-bound mediator [74]. Based on VP and LiP crystal structures (PDB 2BOQ and 1LLP, respectively)...

Ruiz-Duenas FJ, Pogni R, Morales M et al (2009) Protein radicals in fungal versatile peroxidase catalytic tryptophan radical in both Compound I and Compound II and studies on W164Y, W164H and W164S variants. J Biol Chem 284 7986—7994... 

Morimoto A, Tanaka M, Takahashi S et al (1998) Detection of a tryptophan radical as an intermediate species in the reaction of horseradish peroxidase mutant Phe221Trp and hydrogen peroxide. J Biol Chem 273 14753-14760... 

Barrows TP, Bhaskar B, Poulos TL (2004) Electrostatic control of the tryptophan radical in cytochrome c peroxidase. Biochemistry 43 8826-8834... 

In some enzymes, the protein radical appears to participate in substrate oxidation. Evidence exists for the involvement of a surface tryptophan in the oxidation of veratryl alcohol by the ligninase from Phanerochaete chrysosporium [33]. Similarly, tryptophan radicals on the surface of the versatile peroxidases from Pleurotus eryngii and Bjerkandera adjusta [34—36], and a tyrosine in the LiP from Trametes cervina [33], are thought to be involved in substrate oxidation. 

Hiner ANP, Martmez JI, Amao MB et al (2001) Detection of a tryptophan radical in the reaction of ascorbate peroxidase with hydrogen peroxide. Eur J Biochem 268 3091-3098... 

However, recently it has proved possible to positively identify tryptophan radicals in cytochromec peroxidase[147] and tyrosine radicals in ribonucleotide reductase, prostaglandin H synthase and photosystem II of chloroplasts [148], This has been achieved by a combination of the techniques discussed already, but with the powerful, additional non-invasive tool of isotopic substitution. As deuterons (5=1) give different splitting than protons (S = 1/2), substituting different labelled amino-acid residues into the enzyme should reveal the nature of the radical-containing residue. This is easily achieved in an auxotrophic mutant that requires this amino acid to be supplied in the medium. The specific residue can then be identified by site-directed mutagenesis of the evolutionary conserved amino-acid residues [108,149-151]. 

All of these compounds are expected to have ferryl iron with no porphyrin cation radical. As with optical spectroscopy the presence of the distant tryptophan radical in cytochrome c peroxidase compound I appears to have no effect on the MCD spectra. This was confirmed by a direct comparison of cytochrome c peroxidase compounds I and II [172] in the visible region. Tryptophan has a distinct MCD spectrum at 280 nm [173]. However, none of the changes in the UV MCD spectrum that occurred upon compound I formation could be attributed to the formation of the tryptophan radical [174]. 

A theoretical determination of vibrational absorption and Raman spectra of 3-methylindole radicals has been carried out in comparison to experimentally measured spectra for 3-methylindole (Table 28) to provide specific spectroscopic markers for the detection of neutral or cationic tryptophan radicals in biological systems <2001CPH(265)13>. Among isatin derivatives, substitution at C-5 has relatively greater influence on the electron density and the force constant of the amide than of the ketone carbonyl group (Table 29) <2001SAA469>. 

Lendzian, F., Sahlin, M., Macmillan, F., Bittl, R., Fiege, R., PTsch, S., Sj berg, B.-M., Gr%oslund, A., Lubitz, W., and Lassmann, G., 1996, Electronic structure of neutral tryptophan radicals in ribonucleotide reductase studied by EPR and ENDOR spectroscopy. J. Am. Chem. Soc. 118 8111ii8120. 

Putsch, S., Lendzian, F., Ingemarson, R., Homberg, A., Thelander, L., Lubitz, W., Lassmann, G., and Gr%oslund, A., 1999, The iron-oxygen reconstitution reaction in protein R2-tyr-177 mutants of mouse ribonucleotide reductaseoEPR and electron nuclear double resonance studies on a new transient tryptophan radical. J. Biol. Chem. 274 17696nl7704. 

Absorption spectra of phenoxyl radicals derived from biologically important molecules were recorded in numerous cases. The tyrosyl radical was studied by many investigators and its spectrum was used to detect tyrosine oxidation in a protein and to follow intramolecular electron transfer from tyrosine to the tryptophan radical in dipeptides and polypeptides . A number of catecholamines, such as adrenaline and dopa, were also studied by kinetic spectrophotometric pulse radiolysis " ". The absorption spectra of most of these substituted o-semiquinone anion were similar to those of the unsubstituted... 

Santus R., Patterson L.K., Hug G.L., Bazin M., Maziere J.C., Morliere P., Interactions of superoxide anion with enzyme radicals kinetics of reaction with lysozyme tryptophan radicals and corresponding effects on tyrosine electron transfer. Free Rad. Res., 2000,33,383-391. 

Reactions are fast with aromatic residues (k= 10 mol 1 s f). They begin by OH addition to the ring. With phenylalanine, addition occurs preferentially on the ortho position relative to -CH2CHCONH group (55). For tyrosine, addition takes place mostly at the ortho position relative to the phenol function. However, in both cases additions can also be expected on other positions. In tryptophan, the indole ring is more reactive than the phenyl one. OH-adducts may release OH giving phenoxyl (from tyrosine) or indolyl (from tryptophan) radicals whose absorption spectra are well characterized (table 3). 

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