Evidence for formation of diphenylphosphinic peroxy radical intermediate: Spin trapping and chemical reactivity of the new phosphorus radical generated from diphenylphosphinic chloride and superoxide

1990 ◽  
Vol 1 (3) ◽  
pp. 261-265 ◽  
Author(s):  
Sang Chul Lim ◽  
Yong Hae Kim
Keyword(s):  
Chemical Reactivity ◽  
Peroxy Radical ◽  
Spin Trapping ◽  
Radical Intermediate ◽  
Intermediate Spin

Lignin peroxidase structure and function

2001 ◽  
Vol 29 (2) ◽  
pp. 111-116 ◽  
Author(s):  
K. Piontek ◽  
A. T. Smith ◽  
W. Blodig
Keyword(s):  
Lignin Peroxidase ◽  
Structural Changes ◽  
Plant Cell Wall ◽  
Peptide Mapping ◽  
Spin Trapping ◽  
Site Directed Mutagenesis ◽  
Artificial Substrates ◽  
Protein Chemistry ◽  
Redox Potentials ◽  
Radical Intermediate

Lignin peroxidase (LiP) plays a central role in the biodegradation of the plant cell wall constituent lignin. LiP is able to oxidize aromatic compounds with redox potentials higher than 1.4 V (NHE) by single electron abstraction, but the exact redox mechanism is still poorly understood. The finding in our laboratory that the Cβ-atom of Trp171 carries a unique modification led us to initiate experiments to investigate the role of this residue. These experiments, employing crystallography, site-directed mutagenesis, protein chemistry, spin-trapping and spectroscopy, yielded the following results: (i) Trp171 is stereospecifically hydroxylated at its Cβ-atom as the result of an auto-catalytic process, which occurs under turnover conditions in the presence of hydrogen peroxide, (ii) Evidence for the formation of a Trp171 radical intermediate has been obtained using spin-trapping, in combination with peptide mapping and protein crystallography. (iii) Trp171 is very likely to be involved in electron transfer from natural substrates to the haem cofactor via LRET. (iv) Mutagenetic substitution of Trp171 abolishes completely the oxidation activity for veratryl alcohol, but not for artificial substrates. (v) Structural changes in response to the mutation are marginal. Therefore the lack of activity is due to the absence of the redox active indole side chain.

Spin trapping of a free radical intermediate formed during microsomal metabolism of hydrazine

1985 ◽  
Vol 133 (3) ◽  
pp. 1086-1091 ◽  
Author(s):  
Atsuko Noda ◽  
Hiroshi Noda ◽  
Kohji Ohno ◽  
Toshiaki Sendo ◽  
Ayako Misaka ◽  
...  
Keyword(s):  
Free Radical ◽  
Spin Trapping ◽  
Radical Intermediate ◽  
Microsomal Metabolism ◽  
Free Radical Intermediate

scholarly journals Spin-trapping studies on the free-radical products formed by metabolic activation of carbon tetrachloride in rat liver microsomal fractions isolated hepatocytes and in vivo in the rat

1982 ◽  
Vol 204 (2) ◽  
pp. 593-603 ◽  
Author(s):  
E Albano ◽  
K A K Lott ◽  
T F Slater ◽  
A Stier ◽  
M C R Symons ◽  
...  
Keyword(s):  
Free Radical ◽  
Carbon Tetrachloride ◽  
Spin Trap ◽  
Peroxy Radical ◽  
Metabolic Activation ◽  
Spin Trapping ◽  
Metabolic Inhibitors ◽  
Radical Species ◽  
Free Radical Species ◽  
Trichloromethyl Radical

1. The metabolic activation of carbon tetrachloride to free-radical intermediates is an important step in the sequence of disturbances leading to the acute liver injury produced by this toxic agent. Electron-spin-resonance (e.s.r.) spin-trapping techniques were used to characterize the free-radical species involved. 2. Spin trapping was applied to the activation of carbon tetrachloride by liver microsomal fractions in the presence of NADPH, and by isolated intact rat hepatocytes. The results obtained with the spin trap N-benzylidene-2-methylpropylamine N-oxide (‘phenyl t-butyl nitrone’) (PBN) and [13C]carbon tetrachloride provide unequivocal evidence for the formation and trapping of the trichloromethyl free radical in these systems. 3. With the spin trap 2-methyl-2-nitrosopropane, however, the major free-radical species trapped are unsaturated lipid radicals produced by the initiating reaction of lipid peroxidation. 4. Although pulse radiolysis and other evidence support the very rapid formation of the trichloromethyl peroxy radical from the trichloromethyl radical and oxygen, no clear evidence for the trapping of the peroxy radical was obtainable. 5. The effects of a number of free-radical scavengers and metabolic inhibitors on the formation of the PBN-trichloromethyl radical adduct were studied, as were the influences of changing the concentration of PBN and incubation time. 6. High concentrations of the spin traps used were found to have significant effects on cytochrome P-450-mediated reactions; this requires caution in interpreting results of experiments done in the presence of PBN at concentrations greater than 50 mM.

EPR Spin Trapping of a Radical Intermediate in the Urate Oxidase Reaction

2004 ◽  
Vol 23 (8-9) ◽  
pp. 1131-1134 ◽  
Author(s):  
E. Busi ◽  
L. Terzuoli ◽  
R. Basosi ◽  
B. Porcelli ◽  
E. Marinello
Keyword(s):  
Spin Trapping ◽  
Urate Oxidase ◽  
Radical Intermediate ◽  
Epr Spin Trapping ◽  
Oxidase Reaction

scholarly journals Nitric oxide-dependent NAD linkage to glyceraldehyde-3-phosphate dehydrogenase: possible involvement of a cysteine thiyl radical intermediate

1996 ◽  
Vol 319 (2) ◽  
pp. 369-375 ◽  
Author(s):  
Maurizio MINETTI ◽  
Donatella PIETRAFORTE ◽  
A. M. Michela DI STASI ◽  
Cinzia MALLOZZI
Keyword(s):  
Nitric Oxide ◽  
Free Radical ◽  
Active Site ◽  
Superoxide Radical ◽  
Spin Trapping ◽  
Cysteine Residue ◽  
Thiyl Radical ◽  
Radical Intermediate ◽  
No Donors ◽  
High Enzyme

Previous studies have demonstrated that glyceraldehyde-3-phosphate dehydrogenase (GAPDH) undergoes NAD(H) linkage to an active site thiol when it comes into contact with •NO-related oxidants. We found that a free-radical generator 2,2´-azobis-(2-amidinopropane) hydrochloride (AAPH), which does not release either •NO or •NO-related species, was indeed able to induce the NAD(H) linkage to GAPDH. We performed spin-trapping studies with purified apo-GAPDH to identify a putative thiol intermediate produced by AAPH as well as by •NO-related oxidants. As •NO sources we used •NO gas and two •NO-donors, S-nitroso-N-acetyl-D,L-penicillamine and 3-morpholinosydnonimine hydrochloride (SIN-1). Because SIN-1 produces •NO and a superoxide radical simultaneously, we also tested the effects of peroxynitrite. All the •NO-related oxidants were able to induce the linkage of NAD(H) to GAPDH and the formation of a protein free-radical identified as a thiyl radical (inhibited by N-ethylmaleimide). •NO gas and the •NO-donors required molecular oxygen to induce the formation of the GAPDH thiyl radical, suggesting the possible involvement of higher nitrogen oxides. Thiyl radical formation was decreased by the reconstitution of GAPDH with NAD+. Apo-GAPDH was a strong scavenger of AAPH radicals, but its scavenging ability was decreased when its cysteine residues were alkylated or when it was reconstituted with NAD+. In addition, after treatment with AAPH, a thiyl radical of GAPDH was trapped at high enzyme concentrations. We suggest that the NAD(H) linkage to GAPDH is mediated by a thiyl radical intermediate not specific to •NO or •NO-related oxidants. The cysteine residue located at the active site of GAPDH (Cys-149) is oxidized by free radicals to a thiyl radical, which reacts with the neighbouring coenzyme to form Cys-NAD(H) linkages. Studies with the NAD+ molecule radiolabelled in the nicotinamide or adenine portion revealed that both portions of the NAD+ molecule are linked to GAPDH.

EPR Spin Trapping of a Radical Intermediate in the Urate Oxidase Reaction

ChemInform ◽  
2005 ◽  
Vol 36 (9) ◽  
Author(s):  
E. Busi ◽  
L. Terzuoli ◽  
R. Basosi ◽  
B. Porcelli ◽  
E. Marinello
Keyword(s):  
Spin Trapping ◽  
Urate Oxidase ◽  
Radical Intermediate ◽  
Epr Spin Trapping ◽  
Oxidase Reaction

scholarly journals Acetylene, a mammalian metabolite of 1,1,1-trichloroethane

1992 ◽  
Vol 286 (2) ◽  
pp. 353-356 ◽  
Author(s):  
H Dürk ◽  
J L Poyer ◽  
C Klessen ◽  
H Frank
Keyword(s):  
Acute Toxicity ◽  
Rat Liver ◽  
Trichloroacetic Acid ◽  
Spin Trapping ◽  
Radical Intermediate ◽  
Cytochrome P 450

1,1,1-Trichloroethane (TCE) is a widely used industrial solvent of low acute toxicity. It is slowly oxidized to trichloroethanol and trichloroacetic acid by cytochrome P-450-dependent mono-oxygenases. Increased inhalative uptake by rats under hypoxia and spin-trapping experiments indicate that TCE is also reductively metabolized to a radical intermediate. Acetylene is formed as a metabolite, suggesting transfer of an additional electron to form the corresponding carbene. Hypoxia and induction of mixed-function mono-oxygenases accelerate the formation of acetylene. Experiments performed in vitro with rat liver microsomal fractions yield analogous results.

Spatially Resolved Photoelectron Spectroscopy: Recent Progress and Future Plans

1990 ◽  
Vol 48 (2) ◽  
pp. 388-389
Author(s):  
A. M. Bradshaw
Keyword(s):  
Photoelectron Spectroscopy ◽  
Chemical Reactivity ◽  
Target Material ◽  
Orbital Energy ◽  
Light Sources ◽  
Analytical Technique ◽  
Hartree Fock ◽  
Spatially Resolved ◽  
Koopmans Theorem ◽  
Surface Analytical Technique

X-ray photoelectron spectroscopy (XPS or ESCA) was not developed by Siegbahn and co-workers as a surface analytical technique, but rather as a general probe of electronic structure and chemical reactivity. The method is based on the phenomenon of photoionisation: The absorption of monochromatic radiation in the target material (free atoms, molecules, solids or liquids) causes electrons to be injected into the vacuum continuum. Pseudo-monochromatic laboratory light sources (e.g. AlKα) have mostly been used hitherto for this excitation; in recent years synchrotron radiation has become increasingly important. A kinetic energy analysis of the so-called photoelectrons gives rise to a spectrum which consists of a series of lines corresponding to each discrete core and valence level of the system. The measured binding energy, EB, given by EB = hv−EK, where EK is the kineticenergy relative to the vacuum level, may be equated with the orbital energy derived from a Hartree-Fock SCF calculation of the system under consideration (Koopmans theorem).

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