Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

DMSO reductase (DMSOR) from Rhodobacter capsulatus, well-characterised as a molybdoenzyme, will bind tungsten. Protein crystallography has shown that tungsten in W-DMSOR is ligated by the dithiolene group of the two pyranopterins, the oxygen atom of Ser147 plus another oxygen atom, and is located in a very similar site to that of molybdenum in Mo-DMSOR. These conclusions are consistent with W L(III)-edge X-ray absorption, EPR and UV/visible spectroscopic data. W-DMSOR is significantly more active than Mo-DMSOR in catalysing the reduction of DMSO but, in contrast to the latter, shows no significant ability to catalyse the oxidation of DMS.
J Mol Biol 2000 Jun 09
PMID:Dimethylsulfoxide reductase: an enzyme capable of catalysis with either molybdenum or tungsten at the active site. 1083 70

Brain tissue being rich in polyunsaturated fatty acids, is very susceptible to lipid peroxidation. Iron is well known to be an important initiator of free radical oxidations. We propose that the principal route to iron-mediated lipid peroxidations is via iron-oxygen complexes rather than the reaction of iron with hydrogen peroxide, the Fenton reaction. To test this hypothesis, we enriched leukemia cells (K-562 and L1210 cells) with docosahexaenoic acid (DHA) as a model for brain tissue, increasing the amount of DHA from approximately 3 mole % to 32 mole %. These cells were then subjected to ferrous iron and dioxygen to initiate lipid peroxidation in the presence or absence of hydrogen peroxide. Lipid-derived radicals were detected using EPR spin trapping with alpha-(4-pyridyl-1-oxide)-N-t-butylnitrone (POBN). As expected, lipid-derived radical formation increases with increasing cellular lipid unsaturation. Experiments with desferal demonstrate that iron is required for the formation of lipid radicals from these cells. Addition of iron to DHA-enriched L1210 cells resulted in significant amounts of radical formation; radical formation increased with increasing amount of iron. However, the exposure of cells to hydrogen peroxide before the addition of ferrous iron did not increase cellular radical formation, but actually decreased spin adduct formation. These data suggest that iron-oxygen complexes are the primary route to the initiation of biological free radical oxidations. This model proposes a mechanism to explain how catalytic iron in brain tissue can be so destructive.
Cell Mol Biol (Noisy-le-grand) 2000 May
PMID:Iron and free radical oxidations in cell membranes. 1087 52

Spin labeling EPR spectroscopy has been used to characterize light-induced conformational changes of bacteriorhodopsin (bR). Pairs of nitroxide spin labels were attached to engineered cysteine residues at strategic positions near the cytoplasmic ends of transmembrane alpha-helices B, F, and G in order to monitor distance changes upon light activation. The EPR analysis of six doubly labeled bR mutants indicates that the cytoplasmic end of helix F not only tilts outwards, but also rotates counter-clockwise during the photocycle. The direction of the rotation of helix F is the opposite of the clockwise rotation previously reported for bovine rhodopsin. The opposite chirality of the F helix rotation in the two systems is perhaps related to the differences in the cis-trans photoisomerization of the retinal in the two proteins. Using time-resolved EPR, we monitored the rotation of helix F also in real time, and found that the signal from the rotation arises concurrently with the reprotonation of the retinal Schiff base.
J Mol Biol 2000 Dec 15
PMID:Light-induced rotation of a transmembrane alpha-helix in bacteriorhodopsin. 1112 21

The blue dissimilatory nitrite reductase (NiR) from Alcaligenes xylosoxidans is a trimer containing two types of Cu centre, three type 1 electron transfer centres and three type 2 centres. The latter have been implicated in the binding and reduction of nitrite. The Cu ion of the type 2 centre of the oxidized enzyme is ligated by three His residues, and additionally has a co-ordinated water molecule that is also hydrogen-bonded to the carboxyl of Asp(92) [Dodd, Van Beeumen, Eady and Hasnain (1998), J. Mol. Biol. 282, 369-382]. Two mutations of this residue have been made, one to a glutamic acid residue and a second to an asparagine residue; the effects of both mutations on the spectroscopic and catalytic properties of the enzyme have been analysed. EPR spectroscopy revealed that both mutants retained intact type 1 Cu centres with g( parallel)=2.12 (A( parallel)=0 mT) and g( perpendicular)=2.30 (A( perpendicular)=6.4 mT), which was consistent with their blue colour, but differed in their activities and in the spectroscopic properties of the type 2 centres. The D92E mutant had an altered geometry of its type 2 centre such that nitrite was no longer capable of binding to elicit changes in the EPR parameters of this centre. Accordingly, this mutation resulted in a form of NiR that had very low enzyme activity with the artificial electron donors reduced Methyl Viologen and sodium dithionite. As isolated, the EPR spectrum of the Asp(92)-->Asn (D92N) mutant showed no characteristic type 2 hyperfine lines. However, oxidation with iridium hexachloride partly restored a type 2 EPR signal, suggesting that type 2 copper is present in the enzyme but in a reduced, EPR-silent form. Like the Asp(92)-->Glu mutant, D92N had very low enzyme activities with either Methyl Viologen or dithionite. Remarkably, when the physiological electron donor reduced azurin I was used, both mutant proteins exhibited restoration of enzyme activity. The degree of restoration differed for the two mutants, with the D92N derivative exhibiting approx. 60% of the activity seen for the wild-type NiR. These findings suggest that on formation of an electron transfer complex with azurin, a conformational change in NiR occurs that returns the catalytic Cu centre to a functionally active state capable of binding and reducing nitrite.
 ...
PMID:Catalytic and spectroscopic analysis of blue copper-containing nitrite reductase mutants altered in the environment of the type 2 copper centre: implications for substrate interaction. 1113 89

Single crystal EPR studies of VO(II)-doped magnesium potassium Tutton's salt have been carried out at room temperature. The results indicate that the paramagnetic impurity has entered the lattice, both substitutionally and interstitially and the maximum hyperfine for the substitutional site along the a axis corresponds to the minimum hyperfine for interstitial site and vice versa. The spin Hamiltonian parameters obtained from single crystal data for these sites are: Site 1, gparallel = 1.954(1); gperpendicular = 1.998(1), Aparallel = 19.80(2) mT; Aperpendicular = 7.61(2) mT; Site 2, gparallel = 1.997(1); gperpendicular = 1.952(1), Aparallel = 7.66(2) mT; Aperpendicular = 19.85(2) mT. Superhyperfine from ligand protons have been observed at certain orientations for Site 2 impurity. Powder spectrum shows a set of eight parallel and perpendicular features indicating the presence of only one site and these values matched with Site 1 values. From these observations, it has been concluded that the two vanadyl impurities are approximately at right angles to each other. Cooling the sample to 77 K does not change the spectra appreciably. The admixture coefficients have been calculated from Site 1 data, which agree well with the reported values.
Spectrochim Acta A Mol Biomol Spectrosc 2000 Dec
PMID:Single crystal EPR study of VO(II)-doped magnesium. 1114 27

The determination of pH is one of the most important problems in the biochemistry of living organisms, since many of the vital processes of cells and cellular organelles depend on the local pH value. Amongst currently used experimental approaches for the measurement of pH, the application of spin pH probes in combination with EPR spectroscopy is a comparatively new and rapidly developing field. In this article we describe the background, advantages and limitations of the method of spin pH probes, and discuss its recent applications. Availability of a wide variety of pH-sensitive nitroxides with different ranges of pH-sensitivity, labeling group and lipophilicity facilitates their application to a variety of biological systems from subcellular organelles to complex organisms. The recent progress in low-field EPR-based imaging and spectroscopy-based techniques allows spin pH probes to be used for non-invasive in vivo pH measurement and pH-sensitive imaging.
Cell Mol Biol (Noisy-le-grand) 2000 Dec
PMID:Biological applications of spin pH probes. 1115 81

2-fluorovinyl radicals were generated in solid argon by solid-state chemical reactions of mobile F atoms with acetylene and its deuterated analogues. Highly resolved EPR spectra of the stabilized radicals CHF&dbond;(*)CH, CDF&dbond;(*)CD, CHF&dbond;(*)CD, and CDF&dbond;(*)CH were obtained for the first time. The observed spectra were assigned to cis-2-fluorovinyl radical based on excellent agreement between the measured (a(F) = 6.50, a(betaH) = 3.86, a(alphaH) = 0.25 mT) hyperfine constants and those calculated using density functional (B3LYP) theory. Analogous experiments carried out using infrared spectroscopy yielded a complete assignment of the vibrational frequencies. An unusual reversible photochemical conversion is observed in which cis-2-fluorovinyl radicals can be partially converted to 1-fluorovinyl radicals by pulsed laser photolysis at 532 nm. Photolysis at 355 nm converts 1-fluorovinyl back to cis-2-fluorovinyl. High-resolution EPR and infrared spectra of 1-fluorovinyl were obtained for the first time. The measured hyperfine constants (a(F) = 13.71, a(H1) = 4.21, a(H2) = 1.16 mT) are in good agreement with calculated values. Copyright 2001 Academic Press.
J Mol Spectrosc 2001 Feb
PMID:Infrared and EPR Spectroscopic Studies of 2-C(2)H(2)F and 1-C(2)H(2)F Radicals Isolated in Solid Argon. 1116 14

Several new transition metal complexes derived from 1-acetyl-2-(coumariniminecarboxamide-3-yl)hydrazine (HL) have been prepared and characterized by elemental analyses, 1H-NMR, magnetic susceptibility, IR, UV, EPR and thermal analyses. Stereochemistries are proposed for the complexes on the basis of the spectral and magnetic studies. The i.r. data indicate that the carbonyl oxygen of the carboxamide constituents chelating backbone in most complexes. The visible and EPR spectral studies indicated that the Cu(II) complexes have a tetragonal geometry. From the EPR spectrum of the Cu(II) complexes, various parameters were calculated.
Spectrochim Acta A Mol Biomol Spectrosc 2001 Jan
PMID:Spectral studies on metal-ligand bonding in complexes of 1-acetyl-2-(coumariniminecarboxamide-3-yl)hydrazine. 1120 66

Single crystal EPR of Cu(II)-doped low symmetry pentagonal bipyramidal Werner-type clathrate inclusion complexes of Cd(stpy)3(NO3)2 x 1/2stpy(1) and Zn(stpy)3(NO3)2 x 1/2stpy(2) (stpy = trans-4-styrylpyridine) is reported. The spin Hamiltonian parameters are found to be orthorhombic with g33 = 2.298, g22 = 2.108, g11 = 2.066, A33 = 107.3, A22 = 54.4 and A11 = 23.1 x 10(-4) cm(-1) for 1 and g33 = 2.292, g22 = 2.111, g11 = 2.067, A33 = 107.5, A22 = 54.7 and A11 = 22.9 x 10(-4) cm(-1) for 2. Angular variation studies for both 1 and 2 suggest that the Cu(II) ions are substitutionally incorporated in the host lattices. The magnitude of Cu(II) hyperfine coupling constant (A33) in both 1 and 2 are found to be low, in comparison to those of the pure Cu(II) complex, indicative of low symmetry for the substitutional sites in accordance with the crystal data. Such large reductions in Cu(II) hyperfine coupling are explicable in terms of a mixed d(x2 - y2)/dz2 ground state and delocalization of unpaired spin density onto the ligands.
Spectrochim Acta A Mol Biomol Spectrosc 2001 Mar 01
PMID:EPR of Cu(II)-doped seven-coordinate inclusion compounds, M(stpy)3(NO3)2 x 1/2stpy (M = Cd(II) and Zn(II), stpy = trans-4-styrylpyridine): low symmetry effects in admixture of ground states. 1130 May 55

Free radical mediated effects on the gastrointestinal (GI) tract were studied by supplementing 8 mg of iron orally for 15 days to groups of both control (C+) and iron deficient (D+) rats. They were compared with their respective unsupplemented groups C and D. Incorporation of 3H-thymidine into the isolated mucosal cells, as a measure of cell turn over, was lowered significantly in both the D+ and C+ groups compared to their respective controls D and C. It was observed that a single dose of 8 mg of iron given orally to control rats could cause apoptosis of GI tract mucosal cells as shown by the ladder pattern of DNA on electrophoresis. Continuous administration of the same dose of iron for a period of 15 days resulted in necrosis of the GI tract absorptive surface in D+ and C+ rats. In addition to this, a reduction of microvillus height in C+ and complete erosion of the same in D+ were observed by the transmission electron microscopy. EPR spectroscopy identified production of hydroxyl and methoxyl radicals in both the luminal and mucosal contents in the GI tract of rats. These results suggest that when iron is orally administered, free radicals are formed at the site of absorption causing damage to the GI tract mucosa.
Mol Cell Biochem 2001 Mar
PMID:Oral repletion of iron induces free radical mediated alterations in the gastrointestinal tract of rat. 1135 59


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>