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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Kinetics of superoxide radicals generation by a photodynamic therapeutic agent, Hypocrellin A has been studied by EPR-spin trapping technique. The rate constant (k(g)) for superoxide radicals generation by Hypocrellin A was found to be 5.0 x 10(-3) s-1. The first-order rate constant (k1) and the half-life time (t0.5) for DMPO-O2- decay were 2.86 x 10(-3) s-1 and 242.3 s, respectively. It appears that oxyradicals, generated during the photodynamic process, may be associated with the treatment of various skin diseases by photodynamic therapy of Hypocrellin A.
Biochem Mol Biol Int 1996 Apr
PMID:EPR-spin trapping kinetic studies of superoxide radicals produced by photosensitized hypocrellin A. A photodynamic therapeutic agent. 872 97

Acetylcholine-induced, endothelium-dependent relaxation of norepinephrine-precontracted aortic strips, was severely impaired after exposure to a hypoxanthine/xanthine oxidase reaction generating oxygen radicals. This effect was more evident in aortic strips of aging rats (24 months old) in comparison to young rats (3 months old). The addition of authentic .NO (1 microM) completely relaxed aortic strips exposed to oxidative stress both in young and aging rats. In vitro EPR measurements showed that the .NO signal was reduced by enzymatic O2.- generating reaction. The activity of a partial purified preparation of constitutive NO synthase from rat cerebellum was significantly decreased after exposure to exogenous oxygen radicals. Pretreatment of aortic strips with 100 microM alpha-tocopherol-phosphate, produced a significant improvement of acetylcholine-dependent relaxation in the aortic strips exposed to oxidative stress, particularly in the aged vessel. The content of malondialdehyde in aortic tissue did not change after oxidative stress or alpha-tocopherol pretreatment. Alpha-tocopherol was unable to recover the NO synthase activity depressed in vitro by hypoxanthine/xanthine oxidase reaction. This study confirms that an oxidative stress impairs the endothelium-mediated vasodilation. Alpha-tocopherol pretreatment protects the vessel against this damage. The mechanism of action of alpha-tocopherol is unknown, but seems unrelated to an antioxidant activity.
Mol Cell Biochem
PMID:Alpha-tocopherol pretreatment improves endothelium-dependent vasodilation in aortic strips of young and aging rats exposed to oxidative stress. 873 50

Whereas all other members of the extradiol-cleaving catechol dioxygenase family are iron-dependent, the 3,4-dihydroxyphenylacetate 2,3-dioxygenase (MndD) from Arthrobacter globiformis CM-2 is dependent on manganese for catalytic activity. Recently, the endogenous iron ligands of one family member, the 2,3-dihydroxybiphenyl 1,2-dioxygenase (BphC), were identified crystallographically as two histidines and a glutamic acid [Sugiyama, K., et al. (1995) Proc. Jpn. Acad., Ser. B 71, 32-35; Han, et al. (1995) Science 270, 976-980; Senda, T., et al. (1996) J. Mol. Biol. 255, 735-752]. Though BphC and MndD have low overall sequence identity (23%), the three BphC metal ligands are all conserved in MndD (H155, H214, and E266). In order to determine whether these residues also act as ligands to manganese in MndD, site-directed mutants of each were constructed, purified, and analyzed for activity and metal content. Mutations H155A, H214A, and E266Q yielded purified enzymes with specific activities of <0.1% of that of the wild-type dioxygenase and bound 0.4, 1.8, and 33% of the wild-type level of manganese, respectively. The relatively high level of manganese [with a Mn(II) EPR signal distinctly different from that of the wild-type enzyme] observed for E266Q suggests that the glutamine may act as a weak ligand to the metal. Mutant E266D, which retains the potential metal binding capability of a carboxylate group, exhibited 12% of the wild-type activity in crude extracts, suggesting that Mn remains bound; however, this mutant protein was too unstable to be purified and analyzed for metal content. On the basis of the low activity and metal content of mutant proteins, we propose that the conserved residues H155, H214, and E266 ligate manganese in MndD. As is the case with the superoxide dismutases, the extradiol-cleaving catechol dioxygenases appear to utilize identical coordinating residues for their iron- and manganese-dependent enzymes.
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PMID:Manganese(II) active site mutants of 3,4-dihydroxyphenylacetate 2,3-dioxygenase from Arthrobacter globiformis strain CM-2. 904 14

The sulfhydryl group specific spin labels have been used to study the membrane proteins in the bovine and human erythrocyte membranes treated with ozone. The ratio hw/hs, determined from the respective peak amplitudes of the resulting EPR spectra of 3-maleimido-1-oxyl-2,2,5,5-tetramethylpyrrolidine bound to the ozone treated membranes, was shown to be elevated following an increased ozone concentration. The ratio of the central to high-field peak amplitude h0/h-1, a measure of the rotational correlation time, determined from EPR spectra of ozonized membranes covalently labeled with 4-(iodoacetamido)-1-oxyl-2,2,5, 5-tetramethylpyrrolidine was shown to be diminished. The changes in the erythrocyte membranes treated with ozone, observed for both spin labels, indicate a dose dependent increase in the mobility of membrane proteins.
Biochem Mol Biol Int 1997 Feb
PMID:Electron paramagnetic resonance studies of proteins in ozone-treated erythrocyte membranes. 906 75

Structural analysis of delta131delta, a fragment model of the denatured state of staphylococcal nuclease, has been extended by obtaining long-range distance restraints between protein chain segments based on paramagnetic relaxation enhancement methods. PROXYL spin labels were attached at unique cysteine residues introduced at 14 different sites along the polypeptide chain, and the resulting enhancements of amide proton relaxation were measured by NMR spectroscopy. To minimize perturbation of denatured state structure, these labeling sites were chosen on the basis of a high solvent exposure in the native state and a small change in stability and m-value upon mutation of the wild-type residue to cysteine or alanine. EPR spectroscopy confirmed that in all cases the PROXYL label of the modified protein was solvent-exposed and undergoing free isotropic rotation. By quantifying at 500 MHz and 600 MHz the enhancement of both T1 and T2 relaxation for amide protons resolved in a 1H-15N correlation spectrum, the apparent correlation time for the free electron-proton vectors for six PROXYL-labeled proteins could be estimated. With these data plus the enhancements in transverse relaxation rate (R2) for the other eight proteins, the time-averaged, r(-6) weighted distance between the free electron on the unique nitroxide and 30 to 60 amide protons in each protein could be approximated. Inspection of the pattern of R2 enhancements reveals a significant amount of long-range structure in this denatured state, a clear indication that it is not a random coil.
J Mol Biol 1997 Apr 25
PMID:Characterization of long-range structure in the denatured state of staphylococcal nuclease. I. Paramagnetic relaxation enhancement by nitroxide spin labels. 914 49

A universal EPR simulation program has been created by the author, which is based on the following spin Hamiltonian equation: [equation: see text] where D and E are the axial and rhombic zero-field splitting parameters, respectively. The program can be used for simulation of EPR spectra with half-integer electronic spin (S = n/2, n = 3, 5, 7, 9) systems. In this article, the integer spin (S = n/2, n = 2, 4) systems are also considered. The EPR simulation results show that when D > frequency, no EPR signal can be seen from EPR simulation; when D approximately frequency, whichever X/Q/W-band is used, the EPR signal can be seen on the basis of the simulated EPR results presented.
J Mol Graph 1996 Dec
PMID:Why spin = 1, 2 species have no electron paramagnetic resonance signal under normal conditions: possible detection by electron paramagnetic resonance at frequency close to D value? 919 84

By the use of the universal EPR simulation program created by the author, spin S = 3/2 and S = 5/2 systems are studied and their simulated EPR spectra at high frequencies (Q-band for 35 GHz and W-band for 95 GHz) are presented here. The mononuclear Fe3+ in rubredoxin, isolated from Pseudomonas oleovorans (which is an S = 5/2 system with D = 1.76 cm-1 and E/D = 0.28), is extensively studied by EPR spectrum simulation at the Q-band, W-band, and "Z"-band. The molybdenum- and iron-containing protein (MoFe protein), which has g values at g = 4.32, 3.65, and 2.01 (S = 3/2, D = 6.0 cm-1, and E/D = 0.055) at the X-band, is also studied by EPR spectrum simulation at high frequencies.
J Mol Graph 1996 Dec
PMID:Prediction of high-frequency electron paramagnetic resonance spectra of spin S = 3/2, 5/2 systems. 919 86

The aim of this study was to relate changes in the redox state of mitocondrial electron carriers to the 'burst' of oxyradicals in postischemic myocardium. The free radical EPR signals of control and re-oxygenated rat hearts were mainly due to coenzyme Q10, the line width was 0.81 +/- 0.02 mT, and the intensities (1.58 +/- 0.12) x 10(16) and (1.41 +/- 0.13) x 10(16) spins/g. The low-temperature spectra of oxygenated myocardium contained a predominant signal from a S3 Fe-S center and weak signals from N1b, N2, N3, N4 and S1 centers. Global ischemia caused cardinal changes in the redox state of the mitochondrial respiratory chain. The low-temperature EPR spectrum now contained intensive signals from most Fe-S centers. The amount of coenzyme Q10 semiquinones decreased during global ischemia, but the content of flavosemiquinones increased. The line width of the signal of the ischemic heart was 1.28 +/- 0.03 mT, and its intensity corresponded (3.16 +/- 0.94) x 10(16) spins/g. The spin-trapping experiments with TEMPONE-H showed that the rate of oxyradical generation in isolated cardiomyocytes essentially increased after hypoxia or on adding rotenone and antimycin A. It became equal to 4.2 +/- 0.3, 8.2 +/- 0.6 and 7.1 +/- 0.5 nmol/min mg-1 mitochondrial protein, respectively. The maximal stimulatory effect was observed in the presence of both inhibitors. The addition of superoxide dismutase, but not catalase, suppressed the formation of oxyradicals.
Mol Aspects Med 1997
PMID:The redox state of coenzyme Q10 in mitochondrial respiratory chain and oxygen-derived free radical generation in cardiac cells. 926 5

Optical spectroscopy and EPR studies confirm the existence of two b-type hemes in the NarI subunit (cytochrome bnr) of the membrane-bound nitrate reductase (NarGHI) of Escherichia coli. Replacement of His-56 by Arg and His-66 by Tyr results in the loss of the high-potential heme and of the low-potential heme, respectively. These data support the assignment of the axial ligands to the low-potential heme (His-66 and His-187) and to the high-potential heme (His-56 and His-205). This pairing is consistent with the model proposed for NarI of the nitrate reductase of Thiosphaera pantotropha (Berks, B. C., Page, M. D., Richardson, D. J. , Reilly, A., Cavill, A., Outen, F., and Ferguson, S. J. (1995) Mol. Microbiol. 15, 319-331) in which the two bis-histidine ligated hemes are coordinated by conserved His residues of helix II and V. EPR and optical studies suggest that the low-potential heme (Em,7 = +17 mV) and the high-potential heme (Em,7 = +122 mV) are located near the periplasmic side and the cytoplasmic side of the membrane, respectively. Moreover, correct insertion of both hemes into NarI requires anchoring to NarGH.
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PMID:Heme axial ligation by the highly conserved His residues in helix II of cytochrome b (NarI) of Escherichia coli nitrate reductase A. 932 88

Electron paramagnetic resonance imaging (EPRI) is currently being developed at frequencies between 200 MHz and 2 GHz. EPRI can map the in vivo distribution of paramagnetic species, such as water soluble free radicals; nitroxide free radicals are commonly used. EPR images reflect the complexity of metabolic actions on the exogenous delivered nitroxides. Their reduction rate in vivo is affected by parameters such as oxygen concentration, pH and biodistribution. This paper illustrates the main features of low frequency EPRI and reconstruction techniques. Examples of EPR imaging, such as two-dimensional (2D) spatial mapping of the distribution of a nitroxide free radical in phantoms and in whole rat, are given.
Cell Mol Biol (Noisy-le-grand) 1997 Sep
PMID:Water soluble free radicals as biologically responsive agents in electron paramagnetic resonance imaging. 935 28


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