170,799 research outputs found
Fascinated by NMR since 30 years.
No full textThe biographical instances that guided Christian Griesinger toward NMR were early interest in chemistry (enhanced by participation in two chemistry olympiads) and physics, NMR relying on both basic sciences, and contact with NMR during undergraduate studies. History of scientific contributions covered are correlation experiments, three-dimensional NMR, sensitivity enhancement, cross-correlated relaxation, protein dynamics, structural biology, and finally neurodegeneration
H-2-FORMING N-5,N-10-METHYLENETETRAHYDROMETHANOPTERIN DEHYDROGENASE FROM METHANOBACTERIUM-THERMOAUTOTROPHICUM CATALYZES A STEREOSELECTIVE HYDRIDE TRANSFER AS DETERMINED BY 2-DIMENSIONAL NMR-SPECTROSCOPY
No full text5,6,7,8-Tetrahydromethanopterin is a coenzyme playing a key role in the energy metabolism of methanogenic archaea. In Methanobacterium thermoautotrophicum, the reduction of N5,N-10-methenyl-5,6,7,8-tetrahydromethanopterin at C(14a) with H-2 to N5,N-10-methylene-5,6,7,8-tetrahydromethanopterin can be catalyzed by H-2-forming methylenetetrahydromethanopterin dehydrogenase, a new hydrogenase present in most methanogenic archaea, which is unique because it does not contain nickel or iron/sulfur clusters. In this work, the stereochemistry of this enzymatic hydride-transfer reaction is elucidated by means of a series of heteronuclear two-dimensional NMR experiments. It is found that the hydride from H-2 is transferred by the enzyme into the rel-(pro-R) position of the C(14a) methylene group of the reaction product N5,N-10-methylene-5,6,7,8-tetrahydromethanopterin. NMR experiments are described that show that the hydrogen nucleus of the hydride transferred to the oxidized coenzyme partially originates from water. The stereochemical course of this reaction is the same as that for direct hydride transfer. It is demonstrated that the diastereotopic atoms at C(14a) of the reaction product epimerize in an uncatalyzed reaction under the conditions of operation of the enzyme (k = 0.01 s-1 at 58-degrees-C and pH 6.5). On the basis of the known relative configuration of the pterin moiety of 5,6,7,8-tetrahydromethanopterin [Schleucher, J., Schworer, B., Zirngibl, C., Koch, U., Weber, W., Egert, E., Thauer, R. K., & Griesinger, C. (1992) FEBS Lett. 314, 440-444], the absolute configuration of this moiety is tentatively assigned to be (6S,7S, 11R) on the basis of a comparison of the CD spectra of N5,N-10-methenyl-5,6,7,8-tetrahydromethanopterin and its analog N5,N-10-methenyl-5,6,7,8-tetrahydrofolate. Given this absolute configuration of the pterin moiety, the rel-(pro-R) stereochemistry of the C(14a) methylene proton corresponds to the absolute (pro-R) stereochemistry
Measurement of 2J(H,C)- and 3J(H,C)-coupling constants by alpha/beta selective HC(C)H-TOCSY.
No full textItem does not contain fulltextA new heteronuclear NMR pulse sequence for the measurement of nJ(C,H) coupling constants, the alpha/beta selective HC(C)H-TOCSY, is described. It is shown that the S3E element (Meissner et al., 1997a,b) can be used to obtain spin state selective coherence transfer in molecules, in which adjacent CH moieties are labeled with 13C. Application of the alpha/beta selective HC(C)H-TOCSY to a 10 nt RNA tetraloop 5'-CGCUUUUGCG-3', in which the four uridine residues are 13C labeled in the sugar moiety, allowed measurement of two bond and three bond J(C,H) coupling constants, which provide additional restraints to characterize the sugar ring conformation of RNA in cases of conformational averaging
Adiabatic TOCSY for C,C and H,H J-transfer
No full textAdiabatic pulses have been widely used for broadband decoupling and spin inversion at high magnetic fields. In this paper we propose adiabatic pulses and supercycles that can be used at high magnetic fields like 800 or 900 MHz to obtain broadband TOCSY sequences with C,C or H,H J-transfer. The new mixing sequences are equal or even superior to the well known DIPSI-2,3 experiments with respect to bandwidth. They prove robust against pulse miscalibration and B-1 inhomogeneity and are therefore attractive for fully automated spectrometer environments. These adiabatic mixing sequences have been incorporated in a novel z-filter HCCH-TOCSY experiment
Measurement of long range H,C couplings in natural products in orienting media: a tool for structure elucidation of natural products
Full text linkIn this paper we show that water insoluble compounds dissolved in poly-γ-benzyl-glutamate are amenable to the measurement of a number of homo- and heteronuclear dipolar couplings. The sensitivity and experimental precision of dipolar couplings are sufficient to obtain a good match with the structure. In order to achieve the necessary precision for H,C dipolar couplings between protons and carbons that are not directly bound a new method for the measurement of heteronuclear long range couplings is introduced that allows a one-parameter fit to a HSQC-based experiment as reference experiment. The methodology is applied to menthol (1R, 3S, 4R)
Tissue plasminogen activator mediates reverse occlusion plasticity in visual cortex
No full textPreventing visual input to one eye (monocular deprivation) in early postnatal development reduces cortical responses to stimulation of the deprived eye, with a significant loss of thalamocortical connections. These effects are reversible by opening the deprived eye and closing the previously open eye (reverse occlusion). We show that intracortical blockade of tissue plasminogen activator or plasmin selectively prevents recovery of cortical function and thalamic neuron size during reverse occlusion, without affecting the monocular deprivation response. Therefore, a proteolytic cascade consisting of plasmin generated by tissue plasminogen activator may selectively mediate reverse-occlusion-induced cortical plasticity, perhaps via structural remodeling of axons
Ubiquitin Backbone Motion Studied via NHN-C′Cα Dipolar-Dipolar and C′-C′Cα/NHN CSA-Dipolar Cross-Correlated Relaxation.
No full textWhile it is recognized that protein side chains undergo large reorientations, very little is known about the extent and the nature of the motions within the protein backbone. These motions can be studied by chemical shift anisotropy (CSA)-dipolar cross-correlated relaxation rates, the interpretation of which relies on prior knowledge of the CSA principal axis values and directions. Alternatively, dipolar-dipolar cross-correlated relaxation rates can be used. Here we propose a CT-HNCO experiment to measure the sum of the two C'C-alpha/NCalpha dipolar-NHN/C'H-N dipolar cross-correlated relaxation rates. At the same time the experiment gives access to the cross-correlated relaxation rates between C' CSA and the NHN or C'C-alpha dipoles. The complete see of three cross-correlated relaxation rates, measured for the protein ubiquitin, is interpreted in terms of the Gaussian axial fluctuation model of motion. This model provides a good framework for the description of the motions of peptide planes in alpha-helical and rum regions, while a poor fitting of the cross-correlated relaxation data is obtained for beta-sheet regions. The cross-correlated relaxation rates for the alpha-helix peptide planes 23-34 are similar, and their characteristic values suggest the possibility of a concerted motion of the helix or systematic changes in the carbonyl CSA principal axis values and directions
NMR spectroscopic determination of angles alpha and delta in RNA from CH-dipolar coupling, P-CSA cross-correlated relaxation
No full textA new method is introduced to measure the backbone torsion angles alpha and zeta in C-13-labeled oligonucleotides. The experiments relies on the quantification of the cross-correlated relaxation of C,P double and zero quantum coherence caused by the C,H dipolar coupling and the P chemical shift anisotropy. Two-dimensional surfaces that reveal the angular dependence of the cross-correlated relaxation rates depend on the backbone angles alpha and beta as well as epsilon and zeta and are interpreted using torsion angle information for the angles beta and epsilon from experiments measuring (3)J(H,P) and (3)J(C,P) coupling constants. The experiments have been carried out on the 10mer RNA 5'-CGCUUUUGCG-3' that forms a hairpin and in which the four uridine residues are C-13-labeled in the ribofuranoside moiety
Resolution enhancement in spectra of natural products dissolved in weakly orienting media with the help of 1H homonuclear dipolar decoupling during acquisition: Application to 1H-13C dipolar couplings measurements.
No full textIn weakly orienting media such as poly-gamma-benzyl-L-glutamate (PBLG) a polymer that forms a chiral liquid crystal in organic solvents, the spectral resolution for embedded molecules is usually poor because of numerous H-1, 1H dipolar couplings that generally broaden proton spectra. Therefore H-1, C-13 dipolar couplings are difficult or impossible to measure. Here, we incorporate Flip-Flop decoupling during detection into an HSQC experiment. Flip-Flop removes the H-1, H-1 dipolar couplings and scales the chemical shifts of the protons as well as the H-1, C-13 dipolar Couplings during detection. A resolution gain by a factor 1.5-4.2 and improved signal intensity by an average factor of 1.6-1.7 have been obtained. This technique is demonstrated on (+)-menthol dissolved in a PBLG/CDCl3 phase. (c) 2006 Elsevier Inc. All rights reserved
Cholera-Regulativ
No full textden Sanitätsbehörden, den Aerzten und dem Publikum vorgelegt von W. Griesinger ; Max v. Pettenkofer ; C. A. Wunderlic
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