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991.
Siegbahn PE 《Physical chemistry chemical physics : PCCP》2012,14(14):4849-4856
The new high-resolution X-ray structure of photosystem II has allowed more detailed studies than before of water oxidation at the oxygen evolving complex (OEC). In the present study the two final S-transitions of water oxidation are studied. The electron coupled proton transfers are followed from the center of the OEC to Asp61, which is considered as the start of the transfer chain through the protein to the lumenal side. It is found that the proton transfers occur in multiple steps. Structures of intermediates and energy diagrams are derived and compared to experimental observations. Since the new experimental structure of the OEC is very similar to the one suggested earlier by density functional calculations, the O-O bond formation step remains essentially the same as the one suggested five years ago. An interesting new result is that the barrier for proton transfer within the OEC actually competes with the O-O bond formation step of being rate-limiting. 相似文献
992.
In this tutorial review in the thematic series "Acoustofluidics", we discuss the implementation and practice of optical microscopy in acoustofluidic micro-devices. Examples are given from imaging of acoustophoretic manipulation of particles and cells in microfluidic channels, but most of the discussion is applicable to imaging in any lab-on-a-chip device. The discussion includes basic principles of optical microscopy, different microscopy modes and applications, and design criteria for micro-devices compatible with basic, as well as advanced, optical microscopy. 相似文献
993.
Cassimjee KE Humble MS Land H Abedi V Berglund P 《Organic & biomolecular chemistry》2012,10(28):5466-5470
For biocatalytic production of pharmaceutically important chiral amines the ω-transaminase enzymes have proven useful. Engineering of these enzymes has to some extent been accomplished by rational design, but mostly by directed evolution. By use of a homology model a key point mutation in Chromobacterium violaceum ω-transaminase was found upon comparison with engineered variants from homologous enzymes. The variant Trp60Cys gave increased specificity for (S)-1-phenylethylamine (29-fold) and 4'-substituted acetophenones (~5-fold). To further study the effect of the mutation the reaction rates were Swain-Lupton parameterised. On comparison with the wild type, reactions of the variant showed increased resonance dependence; this observation together with changed pH optimum and cofactor dependence suggests an altered reaction mechanism. 相似文献
994.
Haq SR Chi CN Bach A Dogan J Engström Å Hultqvist G Karlsson OA Lundström P Montemiglio LC Strømgaard K Gianni S Jemth P 《Journal of the American Chemical Society》2012,134(1):599-605
Intrinsically disordered proteins are very common and mediate numerous protein-protein and protein-DNA interactions. While it is clear that these interactions are instrumental for the life of the mammalian cell, there is a paucity of data regarding their molecular binding mechanisms. Here we have used short peptides as a model system for intrinsically disordered proteins. Linear free energy relationships based on rate and equilibrium constants for the binding of these peptides to ordered target proteins, PDZ domains, demonstrate that native side-chain interactions form mainly after the rate-limiting barrier for binding and in a cooperative fashion. This finding suggests that these disordered peptides first form a weak encounter complex with non-native interactions. The data do not support the recent notion that the affinities of intrinsically disordered proteins toward their targets are generally governed by their association rate constants. Instead, we observed the opposite for peptide-PDZ interactions, namely, that changes in K(d) correlate with changes in k(off). 相似文献
995.
Due to the lack of a stable technetium isotope, and the high mobility and long half-life, 99Tc is considered to be one of the most important radionuclides in safety assessment of environmental radioactivity as well as nuclear waste management. 99Tc is also an important tracer for oceanographic research due to the high technetium solubility in seawater as TcO4−. A number of analytical methods, using chemical separation combined with radiometric and mass spectrometric measurement techniques, have been developed over the past decades for determination of 99Tc in different environmental samples. This article summarizes and compares recently reported chemical separation procedures and measurement methods for determination of 99Tc. Due to the extremely low concentration of 99Tc in environmental samples, the sample preparation, pre-concentration, chemical separation and purification for removal of the interferences for detection of 99Tc are the most important issues governing the accurate determination of 99Tc. These aspects are discussed in detail in this article. Meanwhile, the different measurement techniques for 99Tc are also compared with respect to advantages and drawbacks. Novel automated analytical methods for rapid determination of 99Tc using solid extraction or ion exchange chromatography for separation of 99Tc, employing flow injection or sequential injection approaches are also discussed. 相似文献
996.
Registration of point sets is done by finding a rotation and translation that produces a best fit between a set of data points and a set of model points. We use robust M-estimation techniques to limit the influence of outliers, more specifically a modified version of the iterative closest point algorithm where we use iteratively re-weighed least squares to incorporate the robustness. We prove convergence with respect to the value of the objective function for this algorithm. A comparison is also done of different criterion functions to figure out their abilities to do appropriate point set fits, when the sets of data points contains outliers. The robust methods prove to be superior to least squares minimization in this setting. 相似文献
997.
Per Christian Hansen James G. Nagy Konstantinos Tigkos 《BIT Numerical Mathematics》2014,54(3):649-671
We describe iterative deblurring algorithms that can handle blur caused by a rotation along an arbitrary axis (including the common case of pure rotation). Our algorithms use a sparse-matrix representation of the blurring operation, which allows us to easily handle several different boundary conditions. We also include robust stopping rules for the iterations. The performance of our algorithms is illustrated with examples. 相似文献
998.
Let m ≥ 0, n ≥ 0 be fixed integers with m + n ≠ 0 and let R be a prime ring with char(R) = 0 or m + n + 1 ≤ char(R) ≠ 2. Suppose that there exists an additive mapping T : R → R satisfying the relation 2T(x m+n+1) = x m T(x) x n + x n T(x)x m for all ${x\in R}$ . In this case T is a two-sided centralizer. 相似文献
999.
A. Algora D. Jordan J. L. Taín B. Rubio J. Agramunt L. Caballero E. Nácher A. B. Perez-Cerdan F. Molina E. Estevez E. Valencia A. Krasznahorkay M. D. Hunyadi J. Gulyás A. Vitéz M. Csatlós L. Csige T. Eronen J. Rissanen A. Saastamoinen I. D. Moore H. Penttilä V. S. Kolhinen K. Burkard W. Hüller L. Batist W. Gelletly A. L. Nichols T. Yoshida A. A. Sonzogni K. Peräjärvi 《Hyperfine Interactions》2014,223(1-3):245-252
The energy associated with the decay of fission products plays an important role in the estimation of the amount of heat released by nuclear fuel in reactors. In this article we present results of the study of the beta decay of some refractory isotopes that were considered important contributors to the decay heat in reactors. The measurements were performed at the IGISOL facility of the University of Jyväskylä, Finland. In these studies we have combined for the first time a Penning trap (JYFLTRAP), which was used as a high resolution isobaric separator, with a total absorption spectrometer. The results of the measurements as well as their consequences for decay heat summation calculations are discussed. 相似文献
1000.
A semisynthetic glutathione peroxidase with high catalytic efficiency. Selenoglutathione transferase
Ren X Jemth P Board PG Luo G Mannervik B Liu J Zhang K Shen J 《Chemistry & biology》2002,9(7):789-794
Glutathione peroxidase (GPX) protects cells against oxidative damage by catalyzing the reduction of hydroperoxides by glutathione (GSH). GPX therefore has potential therapeutic value as an antioxidant, but its pharmacological development has been limited because GPX uses a selenocysteine as its catalytic group and it is difficult to generate selenium-containing proteins with traditional recombinant DNA technology. Here, we show that naturally occurring proteins can be modified to generate GPX activity. The rat theta-class glutathione transferase T2-2 (rGST T2-2) presents an ideal scaffold for the design of a novel GPX catalyst because it already binds GSH and contains a serine close to the substrate binding site, which can be chemically modified to bind selenium. The modified Se-rGST T2-2 efficiently catalyzes the reduction of hydrogen peroxide, and the GPX activity surpasses the activities of some natural GPXs. 相似文献