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331.
Wouters J Oudjama Y Ghosh S Stalon V Droogmans L Oldfield E 《Journal of the American Chemical Society》2003,125(11):3198-3199
We have obtained the three-dimensional X-ray crystallographic structure of a C67A mutant Escherichia coli isopentenylpyrophosphate-dimethylallylpyrophosphate isomerase (EC 5.3.3.2) complexed with the bromohydrin of isopentenylpyrophosphate, at 1.93 A resolution. The overall backbone fold is very similar to that obtained previously for the wild-type enzyme in the presence of a divalent metal cation (Mn2+ or Mg2+). However, in the new structure, there are two metal binding sites, not just one. The first metal binding site is occupied by Mn2+, coordinated to three histidine and two glutamate residues, while the second is occupied by Mg2+, coordinated to two bromohydrin-ligand phosphate oxygens, the carbonyl oxygen of A67, a carboxyl oxygen of E87, and two water molecules. The C3 hydroxyl group of the bromohydrin inhibitor is involved in a short hydrogen bond to the carboxyl group of E116, one of the two Mn-bound glutamates. The structure obtained is consistent with a mechanism of action of the enzyme in which the carboxyl group of E116 protonates the double bond in isopentenylpyrophosphate, forming a carbocation, followed by removal of a C2 proton by the thiolate of C67, in the wild-type enzyme. The inhibition of the enzyme by a wide variety of other potent inhibitors is also readily explained on the basis of the bromohydrin inhibitor structure. 相似文献
332.
Gabriela Ionita Petre Ionita Victor EM. Sahini Constantin Luca 《Journal of inclusion phenomena and macrocyclic chemistry》2001,39(3-4):269-271
The kinetics of oxidation of amino acids (Arg, His, Lys, Phe, Thr and Tyr), a dipeptide (Gly-His), and BSA (bovine serum albumin) by two persistent water soluble free radicals of the hydrazyl type has been studied.The rate decreases in the order Arg>Lys>Tyr>Thr>HisBSAPheGly-His with bothfree radicals. Addition to the reaction mixture of - and -cyclodextrin decreases the oxidation rate, probably due to amino acidencapsulation in the cyclodextrin cavity. -Cyclodextrin protects more efficiently against oxidation than -cyclodextrin. 相似文献
333.
We extend two well-known results on primitive ideals in enveloping
algebras of semisimple Lie algebras, the
Irreducibility
theorem for associated varieties and
Duflo theorem
on primitive ideals, to much wider classes of algebras.
Our general version of the Irreducibility Theorem says that if
A is a positively filtered associative
algebra such that gr A is a commutative
Poisson algebra with finitely many
symplectic leaves, then the associated variety of any primitive ideal in
A is the closure of
a single connected symplectic leaf. Our general version of the Duflo theorem
says that if A is an algebra with
a triangular structure, see § 2, then any primitive ideal in
A is the
annihilator of a simple highest weight module.
Applications to symplectic reflection algebras
and Cherednik algebras are discussed. 相似文献
334.
We describe special asymptotic structures of solutions of the semilinear heat equation
335.
Wallace Feurzeig Gabriel Katz Philip Lewis Victor Steinbok 《International Journal of Computers for Mathematical Learning》2000,5(3):283-284
Volume Contents
Volume Contents 相似文献336.
Stanislav V. Averin Petr I. Kuznetzov Victor A. Zhitov Nikolai V. Alkeev 《Optical and Quantum Electronics》2007,39(3):181-192
Solar-blind MSM photodetectors based on the AlGaN heterostructures have been fabricated and investigated. The influence of
material properties on device parameters is discussed. Effect of different buffer layers on the detector performances has
been examined. Detectors exhibit low dark currents and high sensitivity within the range of 250–290 nm. Effect of optical
excitation energy on GaN-based MSM-detector performance is analyzed and discussed. At high excitation level the detector speed
of response is limited by the field screening caused by the space-charge of the holes. The impulse response of GaN-based MSM-detector
is compared favorably with GaAs MSM-device. 相似文献
337.
Arwen R. Pearson Reinhard Pahl Elena G. Kovaleva Victor L. Davidson Carrie M. Wilmot 《Journal of synchrotron radiation》2007,14(1):92-98
X‐ray exposure during crystallographic data collection can result in unintended redox changes in proteins containing functionally important redox centers. In order to directly monitor X‐ray‐derived redox changes in trapped oxidative half‐reaction intermediates of Paracoccus denitrificans methylamine dehydrogenase, a commercially available single‐crystal UV/Vis microspectrophotometer was installed on‐line at the BioCARS beamline 14‐BM‐C at the Advanced Photon Source, Argonne, USA. Monitoring the redox state of the intermediates during X‐ray exposure permitted the creation of a general multi‐crystal data collection strategy to generate true structures of each redox intermediate. 相似文献
338.
Victor Callegari Philipp M. Nellen Roland Hauert Francisco Hernández-Ramírez 《Applied Surface Science》2007,253(22):8969-8973
Focused ion beam physical sputtering and iodine-enhanced etching of indium phosphide (InP) were performed. Up to 15× enhanced etching rates over sputtering were measured at room temperature, due to the addition of iodine to the sputter-process. Reaction mechanisms and products are discussed and characterized. The reaction is limited by the desorption of indium triiodide (InI3) at room temperature. InI3 has to be removed by sputtering, which simultaneously amorphizes the underlying substrate. Surface roughness and stoichiometry of InP are compared for sputtering and etching. Gallium-contamination and the damaged zone in InP are significantly reduced by iodine-enhanced etching. Based on the reaction mechanisms, an optimum beam scanning strategy is proposed which allows precise microfabrication in reduced time and minimizes damage to the substrate. The method is also applicable for other halide gas etching processes of III-V semiconductors. 相似文献
339.
Phase-matched third-harmonic UV generation using low-order modes in a glass micro-fiber 总被引:1,自引:0,他引:1
Victor Grubsky 《Optics Communications》2007,274(2):447-450
We observe phase-matched third-harmonic generation at 355 nm in a low-order mode of a sub-micron diameter glass fiber. The third-harmonic signal exhibits a sharp resonance for a fiber diameter d = 0.49 ± 0.02 μm, in excellent agreement with the value d = 0.506 μm predicted by theory. The third-harmonic conversion efficiency is 2 × 10−6, and is limited by the pump power (1 kW) and effective fiber length (100 μm). 相似文献
340.
The progress in the field of high resolution X-ray microscopy is caused in particular by the rapid developments of synchrotron radiation sources and X-ray optical elements, by the extension of the energy range, improved designs of X-ray microscopes and scanning X-ray microscopes, the use of CCD detectors with high detective quantum efficiency, the introduction of new imaging techniques, and the development of new fields of application. 相似文献