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61.
Katrin de Graaf Hanna Czajkowska Sabine Rottmann Len C Packman Richard Lilischkis Bernhard Lüscher Walter Becker 《BMC biochemistry》2006,7(1):1-13
Background
Diacylglycerol acyltransferase (DGAT, EC 2.3.1.20) catalyzes the acyl-CoA-dependent acylation of sn-1, 2-diacylglycerol to generate triacylglycerol and CoA. The deduced amino acid sequence of cDNAs encoding DGAT1 from plants and mammals exhibit a hydrophilic N-terminal region followed by a number of potential membrane-spanning segments, which is consistent with the membrane-bound nature of this enzyme family. In order to gain insight into the structure/function properties of DGAT1 from Brassica napus (BnDGAT1), we produced and partially characterized a recombinant polyHis-tagged N-terminal fragment of the enzyme, BnDGAT1(1–116)His6, with calculated molecular mass of 13,278 Da.Results
BnDGAT1(1–116)His6 was highly purified from bacterial lysate and plate-like monoclinic crystals were grown using this preparation. Lipidex-1000 binding assays and gel electrophoresis indicated that BnDGAT1(1–116)His6 interacts with long chain acyl-CoA. The enzyme fragment displayed enhanced affinity for erucoyl (22:1cisΔ13)-CoA over oleoyl (18:1cisΔ9)-CoA, and the binding process displayed positive cooperativity. Gel filtration chromatography and cross-linking studies indicated that BnDGAT1(1–116)His6 self-associated to form a tetramer. Polyclonal antibodies raised against a peptide of 15 amino acid residues representing a segment of BnDGAT1(1–116)His6 failed to react with protein in microsomal vesicles following treatment with proteinase K, suggesting that the N-terminal fragment of BnDGAT1 was localized to the cytosolic side of the ER.Conclusion
Collectively, these results suggest that BnDGAT1 may be allosterically modulated by acyl-CoA through the N-terminal region and that the enzyme self-associates via interactions on the cytosolic side of the ER. 相似文献62.
Construction of a selfadjoint,strictly positive transfer matrix for Euclidean lattice gauge theories
M. Lüscher 《Communications in Mathematical Physics》1977,54(3):283-292
It is shown that physical positivity holds in Wilson's lattice gauge theories, i.e. transition probabilities between gauge invariant states are non-negative and the quantum mechanical Hamiltonian has real eigenvalues only. 相似文献
63.
By means of a spectrum conserving transformation, we show that one of the 3 coefficients in Symanzik's improved action can be chosen freely, if only spectral quantities (masses of stable particles, heavy quark potential etc.) are to be improved. In perturbation theory, the other 2 coefficients are however completely determined and their values are obtained to lowest order.Heisenberg foundation fellow 相似文献
64.
65.
Iron-only hydrogenases are high-efficiency biocatalysts for the synthesis and cleavage of molecular hydrogen. Their active site is a diiron center, which carries CO and CN ligands. Remarkably, the two iron atoms likely are connected by a non-protein azadithiolate (adt = S-CH2-NH-CH2-S). To dwell on the role of the adt in H2 catalysis, a specific biomimetic diiron compound, 1 = [Fe2(mu-adt-CH2-Ph)(CO)4(PMe3)2], with unprecedented positive reduction potential, has been synthesized and crystallized previously. It comprises two protonation sites, the N-benzyl-adt nitrogen that can hold a proton (H) and the Fe-Fe bond that will formally carry a hydride (Hy). We investigated changes in the solution structure of 1 in its four different protonation states (1', [1H]+, [1HHy]2+, and [1Hy]+) by X-ray absorption spectroscopy at the iron K-edge. EXAFS reveals that already protonation at the adt nitrogen atom causes a change of the ligand geometry involving a significant lengthening of the Fe-Fe distance and CO and PMe3 repositioning, respectively, thereby facilitating the subsequent binding of a bridging hydride. Hydride binding clearly is discernible in the XANES spectra of [1HHy]2+ and [1Hy]+. DFT calculations are in excellent agreement with the experimentally derived structural parameters and provide complementary insights into the electronic structure of the four protonation states. In the iron-only hydrogenases, protonation of the putative adt ligand may cause the bridging CO to move to a terminal position, thereby preparing the active site for hydride binding en route to H2 formation. 相似文献
66.
67.
Studying the ω<Emphasis Type="Italic">N</Emphasis> elastic and inelastic cross section with nucleons
Ye.S. Golubeva W. Cassing L.A. Kondratyuk A. Sibirtsev M. Büscher 《The European Physical Journal A - Hadrons and Nuclei》2000,7(2):271-277
We explore the possibility to measure the elastic and inelastic ωN cross section in p+d→d+ω+p
sp and p+A reactions. Our studies indicate that the elastic scattering cross sections can be determined for ω momenta above 1 GeV/c
in p+d reactions by gating on high proton spectator momenta whereas the ωN absorption cross section down to low relative ω momenta is most effectively studied in p+A reactions at beam energies 2.0–2.7 GeV.
Received: 15 October 1999 相似文献
68.
We calculate exactly the contribution of instanton fields to the partition function of
n–1 models in two dimensions. Forn=2, the pure instanton gas is infrared finite, infinitely dense and generates a mass dynamically. Forn3, the gas corresponds to a system with complicatedn-body interactions, whose properties are yet to be explored. 相似文献
69.
Burgdorf T Löscher S Liebisch P Van der Linden E Galander M Lendzian F Meyer-Klaucke W Albracht SP Friedrich B Dau H Haumann M 《Journal of the American Chemical Society》2005,127(2):576-592
Structure and oxidation state of the Ni-Fe cofactor of the NAD-reducing soluble hydrogenase (SH) from Ralstonia eutropha were studied employing X-ray absorption spectroscopy (XAS) at the Ni K-edge, EPR, and FTIR spectroscopy. The SH comprises a nonstandard (CN)Ni-Fe(CN)(3)(CO) site; its hydrogen-cleavage reaction is resistant against inhibition by dioxygen and carbon monoxide. Simulations of the XANES and EXAFS regions of XAS spectra revealed that, in the oxidized SH, the Ni(II) is six-coordinated ((CN)O(3)S(2)); only two of the four conserved cysteines, which bind the Ni in standard Ni-Fe hydrogenases, provide thiol ligands to the Ni. Upon the exceptionally rapid reductive activation of the SH by NADH, an oxygen species is detached from the Ni; hydrogen may subsequently bind to the vacant coordination site. Prolonged reducing conditions cause the two thiols that are remote from the Ni in the native SH to become direct Ni ligands, creating a standardlike Ni(II)(CysS)(4) site, which could be further reduced to form the Ni-C (Ni(III)-H(-)) state. The Ni-C state does not seem to be involved in hydrogen cleavage. Two site-directed mutants (HoxH-I64A, HoxH-L118F) revealed structural changes at their Ni sites and were employed to further dissect the role of the extra CN ligand at the Ni. It is proposed that the predominant coordination by (CN),O ligands stabilizes the Ni(II) oxidation state throughout the catalytic cycle and is a prerequisite for the rapid activation of the SH in the presence of oxygen. 相似文献
70.
S. Barsov M. Büscher M. Hartmann V. Hejny A. Kacharava I. Keshelashvili A. Khoukaz V. Koptev P. Kulessa A. Kulikov I. Lehmann V. Leontyev G. Macharashvili Y. Maeda T. Mersmann S. Merzliakov S. Mikirtytchyants A. Mussgiller D. Oellers H. Ohm F. Rathmann R. Schleichert H. Seyfarth H. Ströher S. Trusov Yu. Valdau P. Wüstner S. Yaschenko C. Wilkin 《The European Physical Journal A - Hadrons and Nuclei》2007,31(1):95-104
The production of ω-mesons in the pp → ppω reaction has been investigated with the COSY-ANKE spectrometer for excess energies of 60 and 92MeV by detecting the two
final protons and reconstructing their missing mass. The large physical background was subtracted using an event-by-event
transformation of the proton momenta between the two energies. Differential distributions and total cross-sections were obtained
after careful studies of possible systematic uncertainties in the overall ANKE acceptance. The results are compared with the
predictions of theoretical models. Combined with data on the φ-meson, a more refined estimate is made of the Okubo-Zweig-Iizuka
rule violation in the φ/ω production ratio. 相似文献