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1.
Flavoproteins are involved in a wide range of biological processes, owing to the versatility of the isoalloxazine moiety of flavin, which can undergo both one- and two-electron reactions with the formation of three oxidation states. Paramagnetic semiquinone radical states are stabilised in some flavoproteins and appear as transient intermediates in the reaction of many others. The apoprotein controls the reactivity of flavin semiquinones, including redox potentials, protonation states and access to substrates. Most flavoproteins are involved in oxidation-reduction processes, but some catalyze different types of reactions involving radical intermediates. Anionic and neutral flavin radicals are found in flavoproteins and are distinguished by their line widths in X-band electron paramagnetic resonance. Electron-nuclear double resonance, electron spin echo envelope modulation and hyperfine sublevel correlation spectroscopy make it possible to observe biological electron transfer and catalysis at the level of the electronic structure of the intermediate states. They provide information about the protein environment of flavin semiquinone radicals and their interactions with nearby nuclear and electron spins. Hyperfine couplings, particularly to the 8-methyl protons on the flavin ring, are a sensitive probe of perturbations of the flavin environment. They demonstrate differences in polarity of the flavin binding site and changes that occur in flavoenzymes during binding of substrates. 相似文献
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Bing-Xin Yang Yi-Han Kao Janos Kirz Chang-Xin Gu R.N. Bhargava D.A. Cammack R.J. Dalby 《Physics letters. A》1985,113(5):283-288
Transmission measurements of the extended X-ray absorption fine structure above the oxygen K-edge have been made by using a new scintillation detection technique. The absorption spectrum is in close resemblance with the total electron yield spectrum recorded at the same time. This new technique is of interest for studies of soft X-ray absorption spectroscopy for thin films of solid materials. 相似文献
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Richard Cammack 《Applied magnetic resonance》2010,37(1-4):257-266
Electron paramagnetic resonance (EPR) spectroscopy can provide answers to significant questions about structure and function in biochemistry. Often EPR spectra of proteins containing transition-metal centers and radicals show the influence of electron spin–spin interactions between paramagnets. Analysis of these spectra provides information about distances and molecular orientations. For small proteins, the shape of the EPR spectra is sensitive to freezing effects, and to changes in the solvent environment; intermolecular spin–spin interactions are also observed. For large complex proteins, details of the EPR spectra are often highly conserved in evolution. Reference spectra of paramagnetic proteins are an aid to identification. The sharing of data is becoming a requirement in the public funding of research, and deposition in public databases is already standard for information such as protein structures and gene sequences. This would require the adoption of standard file formats, such as JCAMP-DX (Joint Committee on Atomic and Molecular Physical Data Exchange) or Bruker BES3T (Bruker EPR Standard for Spectrum Storage and Transfer). An archive of EPR spectra of different types of paramagnetic proteins would assist the identification of paramagnetic centers in biological materials. It would increase the profile of research data, allow comparison of different studies, and further interpretation of data in the light of subsequent discoveries. 相似文献
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Hydrochloride salts of N-substituted-bis-(2-chloroethyl)amines can be condensed with m-methoxyphenyl-acetonitrile or 1-phenyl-2-alkanones under phase-transfer conditions to yield precursors of the powerful analgesic compounds - the ketobemidones. 相似文献
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MK Hossain-Ibrahim K Rezajooi JK MacNally MRJ Mason AR Lieberman PN Anderson 《BMC neuroscience》2006,7(1):8-21
Background
Inflammation around cell bodies of primary sensory neurons and retinal ganglion cells enhances expression of neuronal growth-associated genes and stimulates axonal regeneration. We have asked if inflammation would have similar effects on corticospinal neurons, which normally show little response to spinal cord injury. Lipopolysaccharide (LPS) was applied onto the pial surface of the motor cortex of adult rats with or without concomitant injury of the corticospinal tract at C4. Inflammation around corticospinal tract cell bodies in the motor cortex was assessed by immunohistochemistry for OX42 (a microglia and macrophage marker). Expression of growth-associated genes c-jun, ATF3, SCG10 and GAP-43 was investigated by immunohistochemistry or in situ hybridisation. 相似文献6.
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The nucleide 73Kr has been identified by on-line mass separation as a precursor of β-delayed proton emission. The proton branch is (6.8 ±1.2) × 10−3 proton/decay. The protons populate the ground state and also the first excited 2+ state at 866 keV in 72Se with a relative intensity of (35±9) %. The value of QEC−Bp, where Bp is the proton separation energy for the nucleus 73Br, is found to be 4.85 ±0.30 MeV based on the fraction of proton events preceded by positron decay. 相似文献
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Vincent KA Parkin A Lenz O Albracht SP Fontecilla-Camps JC Cammack R Friedrich B Armstrong FA 《Journal of the American Chemical Society》2005,127(51):18179-18189
A new strategy is described for comparing, quantitatively, the ability of hydrogenases to tolerate exposure to O2 and anoxic oxidizing conditions. Using protein film voltammetry, the inherent sensitivities to these challenges (thermodynamic potentials and rates of reactions) have been measured for enzymes from a range of mesophilic microorganisms. In the absence of O2, all the hydrogenases undergo reversible inactivation at various potentials above that of the H+/H2 redox couple, and H2 oxidation activities are thus limited to characteristic "potential windows". Reactions with O2 vary greatly; the [FeFe]-hydrogenase from Desulfovibrio desulfuricans ATCC 7757, an anaerobe, is irreversibly damaged by O2, surviving only if exposed to O2 in the anaerobically oxidized state (which therefore affords protection). In contrast, the membrane-bound [NiFe]-hydrogenase from the aerobe, Ralstonia eutropha, reacts reversibly with O2 even during turnover and continues to catalyze H2 oxidation in the presence of O2. 相似文献
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