Tyrosine electron paramagnetic resonance

The triplet-state splittings of tyrosine were first observed by electron paramagnetic resonance (EPR) more than two decades ago.l30 32) The initial characterization of the splittings was limited to a measurement of >, a root-mean-square zfs defined by... 

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 Jones CM, Lawrence A, Wardman P, Burkitt MJ (2002) Electron paramagnetic resonance with spin trapping investigation into the kinetics of glutathione oxidation by the superoxide radical re-evaluation of the rate constant. Free Rad Biol Med 32 982-900 Jones CM, Lawrence A, Wardman P, Burkitt MJ (2003) Kinetics of superoxide scavenging by glutathione an evaluation of its role in the removal of mitochondrial superoxide. Biochem Soc Trans 31 1337-1339... 

Abbreviations KMB, 2-keto-methylthiobutyric acid DMPO, the spintrap, 5,5-dimethyl- 1 -pyroline-A -oxide ESR, electron-spin resonance (=electron paramagnetic resonance, EPR) spectroscopy DMSO, dimethyl sulphoxide Phe, phenylalanine Tyr, tyrosine HPLC, high-performance liquid chromatography. 

CEMS = conversion electron Mossbauer spectroscopy DFT = density functional theory EFG = electric field gradient EPR = electron paramagnetic resonance ESEEM = electron spin echo envelope modulation spectroscopy GTO = Gaussian-type orbitals hTH = human tyrosine hydroxylase MIMOS = miniaturized mossbauer spectrometer NFS = nuclear forward scattering NMR = nuclear magnetic resonance RFQ = rapid freeze quench SAM = S -adenosyl-L-methionine SCC = self-consistent charge STOs = slater-type orbitals TMP = tetramesitylporphyrin XAS = X-ray absorption spectroscopy. 

Photosystem II (PSII) contains a remarkably stable tyrosine radical D", located at tyr-160 in the D2 polypeptide, which exhibits a well-known electron paramagnetic resonance (EPR) spectrum, EPR Signal Ilg (1). The function of D" " in the mechanism of photosynthetic H2O oxidation remains unclear despite evidence that it can oxidize the Mn complex, the H20-oxidation catalyst in PSII, from the Sq state to the normally daik-stable Si state (2). Several studies indicate that die oxidation state of the Mn complex influences the electron spin-lattice relaxation rate of D" (3-5), perhaps via a weak dipolar coupling, as suggested by Evelo et al. (5). Hence, the relaxation properties of D may provide a probe for the topology of redox-active sites in the 02-evolving center (OEC) and of the magnetic properties of the Mn complex. 

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