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41.
Cox N Rapatskiy L Su JH Pantazis DA Sugiura M Kulik L Dorlet P Rutherford AW Neese F Boussac A Lubitz W Messinger J 《Journal of the American Chemical Society》2011,133(10):3635-3648
The electronic structures of the native Mn(4)O(x)Ca cluster and the biosynthetically substituted Mn(4)O(x)Sr cluster of the oxygen evolving complex (OEC) of photosystem II (PSII) core complexes isolated from Thermosynechococcus elongatus, poised in the S(2) state, were studied by X- and Q-band CW-EPR and by pulsed Q-band (55)Mn-ENDOR spectroscopy. Both wild type and tyrosine D less mutants grown photoautotrophically in either CaCl(2) or SrCl(2) containing media were measured. The obtained CW-EPR spectra of the S(2) state displayed the characteristic, clearly noticeable differences in the hyperfine pattern of the multiline EPR signal [Boussac et al. J. Biol. Chem.2004, 279, 22809-22819]. In sharp contrast, the manganese ((55)Mn) ENDOR spectra of the Ca and Sr forms of the OEC were remarkably similar. Multifrequency simulations of the X- and Q-band CW-EPR and (55)Mn-pulsed ENDOR spectra using the Spin Hamiltonian formalism were performed to investigate this surprising result. It is shown that (i) all four manganese ions contribute to the (55)Mn-ENDOR spectra; (ii) only small changes are seen in the fitted isotropic hyperfine values for the Ca(2+) and Sr(2+) containing OEC, suggesting that there is no change in the overall spin distribution (electronic coupling scheme) upon Ca(2+)/Sr(2+) substitution; (iii) the changes in the CW-EPR hyperfine pattern can be explained by a small decrease in the anisotropy of at least two hyperfine tensors. It is proposed that modifications at the Ca(2+) site may modulate the fine structure tensor of the Mn(III) ion. DFT calculations support the above conclusions. Our data analysis also provides strong support for the notion that in the S(2) state the coordination of the Mn(III) ion is square-pyramidal (5-coordinate) or octahedral (6-coordinate) with tetragonal elongation. In addition, it is shown that only one of the currently published OEC models, the Siegbahn structure [Siegbahn, P. E. M. Acc. Chem. Res.2009, 42, 1871-1880, Pantazis, D. A. et al. Phys. Chem. Chem. Phys.2009, 11, 6788-6798], is consistent with all data presented here. These results provide important information for the structure of the OEC and the water-splitting mechanism. In particular, the 5-coordinate Mn(III) is a potential site for substrate 'water' (H(2)O, OH(-)) binding. Its location within the cuboidal structural unit, as opposed to the external 'dangler' position, may have important consequences for the mechanism of O-O bond formation. 相似文献
42.
Musiol EM Härtner T Kulik A Moldenhauer J Piel J Wohlleben W Weber T 《Chemistry & biology》2011,18(4):438-444
In the biosynthesis of complex polyketides, acyltransferase domains (ATs) are key determinants of structural diversity. Their specificity and position in polyketide synthases (PKSs) usually controls the location and structure of building blocks in polyketides. Many bioactive polyketides, however, are generated by trans-AT PKSs lacking internal AT domains. They were previously believed to use mainly malonyl-specific free-standing ATs. Here, we report a mechanism of structural diversification, in which the trans-AT KirCII regiospecifically incorporates the unusual extender unit ethylmalonyl-CoA in kirromycin polyketide biosynthesis. 相似文献
43.
Alexey M. Kulik 《Journal of Theoretical Probability》2011,24(1):1-38
General sufficient conditions are given for absolute continuity and convergence in variation of the distributions of the functionals
on the probability space generated by a Poisson point measure. The phase space of the Poisson point measure is supposed to
be of the form
\mathbbR+×\mathbbU{\mathbb{R}}^{+}\times{\mathbb{U}}, and its intensity measure to equal dt
Π(du). We introduce the family of time stretching transformations of the configurations of the point measure. Sufficient conditions for absolute continuity and convergence in variation are
given in terms of the time stretching transformations and the relative differential operators. These conditions are applied
to solutions of SDEs driven by Poisson point measures, including SDEs with non-constant jump rate. 相似文献
44.
45.
The deformation of chemical bonds in polymer molecules of surface layers of samples, boundary layers between supramolecular aggregates, and boundary layers between polymers and solids in polymer composites is investigated using IR and Raman spectroscopy. It is found that the chemical bonds are elongated on a free surface and in boundary layers between supramolecular aggregates. By contrast, the chemical bonds are contracted in boundary layers between polymers and solids. The concentration and the strain of excited chemical bonds (strained to approximately a theoretical ultimate elongation) are increased on the free surface and in the boundary layers between supramolecular aggregates, whereas the concentration and the strain of excited chemical bonds in the boundary layers between polymers and solids are decreased. These effects are explained by the changes in the atomic vibrations in the surface and boundary layers. 相似文献
46.
G. S. Vorobjov A. A. Borisenko Ye. V. Belousov V. G. Korzh I. A. Kulik K. A. Pushkarev 《International Journal of Infrared and Millimeter Waves》1998,19(2):243-250
The new method for metering of the static parameters of the axially symmetric electron beams in the devices of the extremely high frequency (EHF) range is proposed in the paper. The method is based on using properties of the transition radiation of the optical range. The transition radiation appears when bombarding a metallic target electrode with electrons. Results of the meterings on distribution of current beam density by way of this method are given. The results are compared with the trajectory analysis when moving the electrons in the field of the investigated electron-optical system. 相似文献
47.
48.
A. M. Kulik 《Ukrainian Mathematical Journal》1995,47(7):1074-1084
We give a sequence of stochastic integro-differential equations that approximates a stochastic differential equation with an anticipating initial condition and localized Skorokhod stochastic integral. A sequence of solutions of these equations is obtained. The convergence of this sequence to a certain process implies that this process is a solution (generally speaking, local) of the original equation.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 47, No. 7, pp. 936–945, July, 1995. 相似文献
49.
A. I. Slutsker V. I. Vettegren V. L. Gilyarov G. Dadobaev V. B. Kulik L. S. Titenkov 《Physics of the Solid State》2002,44(10):1936-1943
The temperature dependences of the transverse expansion ?⊥(T) and the longitudinal contraction ?‖(T) (with respect to the axes of chain molecules) in large-sized poly(ethylene) (PE) crystal grains (100×60×60 nm) are measured using x-ray diffraction in the temperature range 5–380 K. The temperature dependence of the elongation of the molecular skeleton ?C(T) is obtained by Raman spectroscopy. It is found that the dependences ?⊥(T), ?‖(T), and ?C(T) exhibit a similar specific nonlinear behavior. Analysis of these dependences indicates that the nonlinearity is associated with the quantum statistics of transverse vibrations. The energies and amplitudes of zero-point (at T=0) transverse (torsional and bending) vibrations and the relevant zero-point components ?‖(0) and ?C(0) are estimated. It is revealed that the zero-point components make a considerable contribution to the dynamics of the PE crystal up to the melting temperature (~400 K). 相似文献
50.