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- Assarsson, Maria, et al.
(författare)
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Restoring proper radical generation by azide binding to the iron site of the E238A mutant R2 protein of ribonucleotide reductase from Escherichia coli.
- 2001
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 276:29, s. 26852-26859
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Tidskriftsartikel (refereegranskat)abstract
- The enzyme activity of Escherichia coli ribonucleotide reductase requires the presence of a stable tyrosyl free radical and diiron center in its smaller R2 component. The iron/radical site is formed in a reconstitution reaction between ferrous iron and molecular oxygen in the protein. The reaction is known to proceed via a paramagnetic intermediate X, formally a Fe(III)-Fe(IV) state. We have used 9.6 GHz and 285 GHz EPR to investigate intermediates in the reconstitution reaction in the iron ligand mutant R2 E238A with or without azide, formate, or acetate present. Paramagnetic intermediates, i.e. a long-living X-like intermediate and a transient tyrosyl radical, were observed only with azide and under none of the other conditions. A crystal structure of the mutant protein R2 E238A/Y122F with a diferrous iron site complexed with azide was determined. Azide was found to be a bridging ligand and the absent Glu-238 ligand was compensated for by azide and an extra coordination from Glu-204. A general scheme for the reconstitution reaction is presented based on EPR and structure results. This indicates that tyrosyl radical generation requires a specific ligand coordination with 4-coordinate Fe1 and 6-coordinate Fe2 after oxygen binding to the diferrous site.
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- Haeggström, JZ, et al.
(författare)
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Functional properties and molecular architecture of leukotriene A4 hydrolase, a pivotal catalyst of chemotactic leukotriene formation
- 2002
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Ingår i: TheScientificWorldJournal. - : Hindawi Limited. - 1537-744X. ; 2, s. 1734-49
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Tidskriftsartikel (refereegranskat)abstract
- The leukotrienes are a family of lipid mediators involved in inflammation and allergy. Leukotriene B4is a classical chemoattractant, which triggers adherence and aggregation of leukocytes to the endothelium at only nM concentrations. In addition, leukotriene B4modulates immune responses, participates in the host defense against infections, and is a key mediator of PAF-induced lethal shock. Because of these powerful biological effects, leukotriene B4 is implicated in a variety of acute and chronic inflammatory diseases, e.g., nephritis, arthritis, dermatitis, and chronic obstructive pulmonary disease. The final step in the biosynthesis of leukotriene B4is catalyzed by leukotriene A4hydrolase, a unique bifunctional zinc metalloenzyme with an anion-dependent aminopeptidase activity. Here we describe the most recent developments regarding our understanding of the function and molecular architecture of leukotriene A4hydrolase.
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- O'Shea, J. N., et al.
(författare)
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Hydrogen-bond induced surface core-level shift in pyridine carboxylic acids
- 2001
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 486:3, s. 157-166
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Tidskriftsartikel (refereegranskat)abstract
- Intermolecular hydrogen bonding in thick films of pyridine carboxylic acids (isonicotinic; picolinic and bi-isonicotinic acid) evaporated onto rutile TiO2(1 1 0) has been investigated with X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. These molecules are shown to be strongly H-bonded in the condensed phase, and a surface core-level shift is observed due to the presence of non-H-bonded nitrogen atoms in the surface layer. Density functional theory calculations are used to relate the experimental data to the proposed bonding configurations based on the surface termination of the known equilibrium solid-state structure. A kinetic barrier, attributed to the high degree of molecular orientation required for the formation of extended H-bonding networks, has also been investigated.
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