The electron spin resonance spectrum of the tyrosyl radical

Sealy, Roger C.; Harman, Laura S.; West, Paul R.; Mason, Ronald P.

doi:10.1021/ja00298a001

Cited by 96 publications

(90 citation statements)

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“…8 in SI). The notable inequivalence of these β-methylene hydrogen couplings demonstrates the presence of the chiral center in the free radical as is the case in L-tyrosine 16 . Loss of either the carboxyl or amino group would remove the asymmetry and make the β-methylene hydrogens equivalent as observed in the ESR spectrum of tryptamine (Fig.…”

Section: Esr Analyses Of Related Compoundsmentioning

confidence: 83%

l-Tryptophan Radical Cation Electron Spin Resonance Studies: Connecting Solution-Derived Hyperfine Coupling Constants with Protein Spectral Interpretations

et al. 2008

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Fast-flow electron spin resonance (ESR) spectroscopy has been used to detect a free radical formed from the reaction of L-tryptophan with Ce 4+ in an acidic aqueous environment. Computer simulations of the ESR spectra from L-tryptophan and several isotopically modified forms strongly support the conclusion that the L-tryptophan radical cation has been detected by ESR for the first time. The hyperfine coupling constants (HFCs) determined from the well-resolved isotropic ESR spectra support experimental and computational efforts to understand L-tryptophan's role in protein catalysis of oxidation-reduction processes. L-tryptophan HFCs facilitated the simulation of fast-flow ESR spectra of free radicals from two related compounds, tryptamine and 3-methylindole. Analysis of these three compounds' β-methylene hydrogen HFC data along with equivalent L-tyrosine data has led to a new computational method that can distinguish between these two amino acid free radicals in proteins without dependence on isotope labeling, electron nuclear double resonance or high-field ESR. This approach also produces geometric parameters (dihedral angles for the β-methylene hydrogens) which should facilitate protein site assignment of observed L-tryptophan radicals as has been done for L-tyrosine radicals.

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Section: Esr Analyses Of Related Compoundsmentioning

confidence: 83%

l-Tryptophan Radical Cation Electron Spin Resonance Studies: Connecting Solution-Derived Hyperfine Coupling Constants with Protein Spectral Interpretations

et al. 2008

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“…However, the lineshape of the Zt/Dt EPR spectrum does not strongly resemble that of the tyrosine radical in ribonucleotide reductase. This lack of similarity may arise from sensitivity of the methylene proton hyperfine interactions to the dihedral angle that measures their orientation with respect to the phenol ring (45,57). In fact, the EPR hyperfine couplings ofEscherichia coli ribonucleotide reductase and of bacteriophage T4 ribonucleotide reductase are quite different; this difference has been accounted for by variation in this dihedral angle (45).…”

Section: Discussionmentioning

confidence: 99%

“…This lack of similarity may arise from sensitivity of the methylene proton hyperfine interactions to the dihedral angle that measures their orientation with respect to the phenol ring (45,57). In fact, the EPR hyperfine couplings ofEscherichia coli ribonucleotide reductase and of bacteriophage T4 ribonucleotide reductase are quite different; this difference has been accounted for by variation in this dihedral angle (45). A possible interpretation of the apparent 1:3:3:1 ratio of partially resolved hyperfine lines in the oriented D+ spectrum (13,14) may involve accidental degeneracy in the coupling constants of three protons, one or two of which are methylene protons.…”

Section: Discussionmentioning

confidence: 99%

Tyrosine radicals are involved in the photosynthetic oxygen-evolving system.

Barry

Babcock

1987

Proc. Natl. Acad. Sci. U.S.A.

418

312

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In addition to the reaction-center chlorophyll, at least two other organic cofactors are involved in the photosynthetic oxygen-evolution process. One of these cofac.tors, called "Z," transfers electrons from the site of water oxidation to the reaction center of photosystem II. The other species, "D," has an uncertain function but gives rise to the stable EPR signal known as signal II. ZV and D+ have identical EPR spectra and are generally assumed to arise from species with the same chemical structure. Results from a variety of experiments have suggested that Z and D are plastoquinones or plastoquinone derivatives. In general, however, the evidence to support this assignment is indirect. To address this situation, we have developed more direct methods to assign the structure of the ZV/Dt radicals. By selective in vivo deuteration of the methyl groups of plastoquinone in cyanobacteria, we show that hyperfine couplings from the methyl protons cannot be responsible for the partially resolved structure seen in the Dt EPR spectrum. That is, we verify by extraction and mass spectrometry that quinones are labeled in algae fed deuterated methionine, but no change is observed in the line shape of signal II.Considering the spectral properties ofthe Dt radical, a tyrosine origin is a reasonable alternative. In a second series of experiments, we have found that deuteration of tyrosine does indeed narrow the Dt signal. Extraction and mass spectral analysis of the quinones in these cultures show that they are not labeled by tyrosine. These results eliminate a plastoquinone origin for Dt; we conclude instead that Dt, and most likely Zt, are tyrosine radicals.In plant and algal photosynthesis, photosystem II (PSII) catalyzes the light-induced oxidation of water and reduction of plastoquinone. The smallest purified unit that is capable of carrying out this reaction consists of seven polypeptides and contains chlorophyll, plastoquinone, manganese, and several other bound cofactors (for review, see refs. 1 and 2). Water oxidation occurs at a site that contains a cluster of four Mn atoms. This center is interfaced to the photochemically active PSII reaction-center chlorophyll, P680, by at least one intermediate electron carrier, which is usually designated The oxidized form of this cofactor, Zt, has a light-induced EPR signal that identifies it as an organic radical (3-6). A variety of kinetic data indicates that Z reduces P680+ directly and that the resulting Zt species is in turn reduced by the manganese ensemble (refs. 1 and 2, but see refs. 7 and 8). In addition to the EPR signal from Z+, PSII preparations also show a stable EPR signal (signal II) with the same lineshape as Zt (9). The radical giving rise to this spectrum is now usually referred to as "D+". Recent data reported by Styring and Rutherford suggest that D may be involved in maintaining the integrity of the manganese complex (10).Because the Zt and Dt EPR spectra are identical, it is generally assumed that Z and D are species that have the same chemical str...

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“…4). Both CysSO ⅐ and GSO ⅐ have two ␤-methylene hydrogens, but in the latter, a hindered rotation of the methylene group that is adjacent to a chiral center is likely to result in the magnetic nonequivalence (44,45) reflected in the different hyperfine splitting constants (a H ) obtained for its two hydrogens (Fig. 4B).…”

Section: Oxidation Of Gsh and Cysteine-to Evaluate The Effects Of Hcomentioning

confidence: 99%

Carbon Dioxide Stimulates the Production of Thiyl, Sulfinyl, and Disulfide Radical Anion from Thiol Oxidation by Peroxynitrite

Bonini

Augusto

2001

Journal of Biological Chemistry

174

105

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Reaction of peroxynitrite with the biological ubiquitous CO 2 produces about 35% yields of two relatively strong one-electron oxidants, CO 3 . and ⅐ NO 2 , but the remaining of peroxynitrite is isomerized to the innocuous nitrate. Partial oxidant deactivation may confound interpretation of the effects of HCO 3 ؊ /CO 2 on the oxidation of targets that react with peroxynitrite by both one-and two-electron mechanisms. Thiols are example of such targets, and previous studies have reported that HCO 3 ؊ / CO 2 partially inhibits GSH oxidation by peroxynitrite at pH 7.4. To differentiate the effects of HCO 3 ؊ /CO 2 on twoand one-electron thiol oxidation, we monitored GSH, cysteine, and albumin oxidation by peroxynitrite at pH 5.4 and 7.4 by thiol disappearance, oxygen consumption, fast flow EPR, and EPR spin trapping. Our results demonstrate that HCO 3 ؊ /CO 2 diverts thiol oxidation by peroxynitrite from two-to one-electron mechanisms particularly at neutral pH. At acid pH values, thiol oxidation to free radicals predominates even in the absence of HCO 3 ؊ /CO 2 . In addition to the previously characterized thiyl radicals (RS ⅐ ), we also characterized radicals derived from them such as the corresponding sulfinyl (RSO ⅐ ) and disulfide anion radical (RSSR ⅐ ؊ ) of both GSH and cysteine. Thiyl, RSO ⅐ and RSSR ⅐ ؊ are reactive radicals that may contribute to the biodamaging and bioregulatory actions of peroxynitrite.Peroxynitrite 1 (ONOO Ϫ ϩ ONOOH), which is formed by the fast reaction between ⅐ NO and O 2 . , has been receiving increasing attention as a mediator of human diseases and as a toxin against invading microorganisms (1-5). The compound is a potent oxidant that is able to oxidize and nitrate a variety of biological targets by mechanisms that are presently being elucidated (6 -16). In general terms, peroxynitrite-mediated oxidations are either bimolecular, first order on peroxynitrite and biomolecule concentration, or unimolecular, first order on peroxynitrite and independent of biomolecule concentration. Bimolecular processes can result in product yield either around stoichiometry and over, as is the case for thiol oxidation (17), or around 35% , as is the case for carbon dioxide (CO 2 ) oxidation (10, 14 -16). Presently, most investigators accept that product yields around 30% are characteristic of peroxynitrite-mediated free radical processes. Indeed, it has been established that ONOO Ϫ protonation (pK a ϭ 6.6) leads to its fast decomposition (k ϭ 0.17 s Ϫ1 at pH 7.4) to yield approximately 70% nitrate and 30% hydroxyl radical ( ⅐ OH) and nitrogen dioxide ( ⅐ NO 2 ) (Fig. 1, path 1) (7)(8)(9)(11)(12)(13)(14). These radicals are the species responsible for peroxynitrite-mediated unimolecular oxidations. In the presence of HCO 3 Ϫ , ONOO Ϫ decomposes much faster because of its reaction with CO 2 (k ϭ 2.6 ϫ 10 4 M Ϫ1 s Ϫ1 at pH 7.4, 25°C) (18, 19) to produce approximately 65% nitrate and 35% carbonate radical anion (CO 3 . ) and ⅐ NO 2 (Fig. 1, path 2) (10, 14 -16).The fast rate constant of this reaction and...

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The electron spin resonance spectrum of the tyrosyl radical

Cited by 96 publications

References 2 publications

l-Tryptophan Radical Cation Electron Spin Resonance Studies: Connecting Solution-Derived Hyperfine Coupling Constants with Protein Spectral Interpretations

l-Tryptophan Radical Cation Electron Spin Resonance Studies: Connecting Solution-Derived Hyperfine Coupling Constants with Protein Spectral Interpretations

Tyrosine radicals are involved in the photosynthetic oxygen-evolving system.

Carbon Dioxide Stimulates the Production of Thiyl, Sulfinyl, and Disulfide Radical Anion from Thiol Oxidation by Peroxynitrite

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