Near Uv‐induced Free Radicals in Ocular Lens, Studied by Esr and Spin Trapping

Abstract

An electron spin resonance (ESR) study on UV-photolysis of human and canine lens nuclei was carried out at room temperature. (1) At least two kinds of free radical signals, a narrow signal and a broad one, were detected at around g = 2.004. The latter is similar to that observed upon irradiation of a model solution containing both tryptophan and cysteine. (2) Two spin adducts were detected upon irradiation of canine lens in the presence of a spin trapping reagent (DMPO, 5,5-dimethyl-1-pyrroline N-oxide), i.e. a spin adduct of sulphur-centered radical (most likely glutathione thiyl radical) and the protonated adduct of solvated electron (presumably due to photo-ionization of tryptophan). (3) A tentative and simplified reaction mechanism of UV-induced damage is discussed on the basis of these observations.

Direct ESR detection or peroxynitrite-induced tyrosine-centred protein radicals in human blood plasma

“…To our knowledge this is the first report showing that peroxynitrite induces a g l 2n004 signal assigned to a radical centred on protein Tyr residues. This study may be of help in the characterization of similar radicals detected in haemoproteins or in tissues by direct ESR at room temperature [29,42,49].…”

The first ESR observation of radical species generated under pulsed electric fields processing

“…ESR spectra simulations were made using a program created by Hagen (Biomolecular EPR Spectroscopy Software). The hyperfine splitting constants were compared with published values tabulated in the Spin Trapping Database at http:// esr.niehs.nih.gov/stdb/index.cfm (Murakami, Okazaki, & Shiga, 1989). …”

Distinguishing Features of Indolyl Radical and Radical Cation: Implications for Tryptophan Radical Studies

“…4 Tryptophan and tryptamines also act as endogenous radical scavengers to protect proteins from oxidative damage, 5 associated with carcinogenicity 6 and aging. 7 In addition to appearing in chemically- 8,9 and radiatively-damaged proteins, [10][11][12][13][14][15] tyrosine phenoxyl and tryptophan indolyl radicals have been detected in a number of enzymes and have been recognized as catalytically relevant redox agents. [16][17][18][19][20] Tryptophan radicals or radical cations, for example, are believed to participate in electron transfer in cytochrome c peroxidase, 21,22 DNA photolyase, 23,24 galactose oxidase, 17 and perhaps ribonucleotide reductase.…”

“…Tryptophan and tryptamines also act as endogenous radical scavengers to protect proteins from oxidative damage, associated with carcinogenicity and aging . In addition to appearing in chemically- 8,9 and radiatively-damaged proteins, − tyrosine phenoxyl and tryptophan indolyl radicals have been detected in a number of enzymes and have been recognized as catalytically relevant redox agents. − Tryptophan radicals or radical cations, for example, are believed to participate in electron transfer in cytochrome c peroxidase, , DNA photolyase, , galactose oxidase, and perhaps ribonucleotide reductase. , The tryptophan-derived radicals are typically identified by comparing their spectral properties − with experimental or calculated features of the corresponding indolyl radical cation (IndH •+ , shown in 1a along with the conventional atom numbering for indole) or indolyl radical (Ind • , see 1b ).Distinguishing the tryptophan radical (Trp • ) from the tryptophan radical cation (TrpH •+ ) in proteins is important because the radical's identity determines the details of its reactivity. The distinction is complicated, however, by noncovalent contacts involving Trp • or TrpH •+ in proteins ,− and by conflicting information for Ind • and IndH •+ .…”