102 research outputs found
S-adenosyl-l-methionine: (S) -7,8,13, 14-tetrahydroberberine--n-methyltransferase, a branch point enzyme in the biosynthesis of benzophenanthridine and protopine alkaloids.
The enzyme which transfers the CH3-group of S-adenosylmethionine to the nitrogen atom of (S)-tetrahydroberberine and (S)-stylopine is found to occur in a number of plant cell cultures originating from species containing alkaloids; it is located at an important branch point in isoquinoline alkaloid biosynthesis
Enzymatic formation of protopines by a microsomal cytochrome P-450 system of Corydalis vaginans
A microsomal cytochrome P-450-NADPH dependent enzyme which hydroxylates stereo- and regiospecifically carbon atom 14 of (S)- -N- methyltetrahydroprotoberberines has been discovered in a number of plant cell cultures originating from species containing protopine alkaloids; the monooxygenase was solubilized, partially purified (100-fold) and characterized
S-adenosyl-L-methionine: (S)-scoulerine 9-O-methyltransferase, a highly stereo- and regio-specific enzyme in tetrahydroprotoberberine biosynthesis
Suspension cultures of Berberis species are useful sources for the detection and isolation of a new enzyme which transfers the methyl group from S-adenosyl-L-methionine specifically to the 9-position of the (S)-enantiomer of scoulerine, producing (S)-tetrahydrocolumbamine. The enzyme was enriched 27-fold; it is not particle bound, has a pH optimum of 8.9, a molecular weight of 63 000 and shows a high degree of substrate specificity
Biosynthesis of the protoberberine alkaloid jatrorrhizine
Feeding experiments with distant single or doubly labelled precursors show that the methylene dioxy group of berberine is opened in the formation of jatrorrhizine
Valence and magnetic instabilities in Sm compounds at high pressures
We report on the study of the response to high pressures of the electronic
and magnetic properties of several Sm-based compounds, which span at ambient
pressure the whole range of stable charge states between the divalent and the
trivalent. Our nuclear forward scattering of synchrotron radiation and specific
heat investigations show that in both golden SmS and SmB6 the pressure-induced
insulator to metal transitions (at 2 and about 4-7 GPa, respectively) are
associated with the onset of long-range magnetic order, stable up to at least
19 and 26 GPa, respectively. This long-range magnetic order, which is
characteristic of Sm(3+), appears already for a Sm valence near 2.7. Contrary
to these compounds, metallic Sm, which is trivalent at ambient pressure,
undergoes a series of pressure-induced structural phase transitions which are
associated with a progressive decrease of the ordered 4f moment.Comment: 15 pages (including 7 figures) submitted to J. Phys.: Condens. Matte
Double-spiral magnetic structure of the Fe/Cr multilayer revealed by nuclear resonance scattering
We have studied the magnetization depth profiles in a [57Fe(dFe)/Cr(dCr)]x30
multilayer with ultrathin Fe layers and nominal thickness of the chromium
spacers dCr 2.0 nm using nuclear resonance scattering of synchrotron radiation.
The presence of a broad pure-magnetic half-order (1/2) Bragg reflection has
been detected at zero external field. The joint fit of the reflectivity curves
and Mossbauer spectra of reflectivity measured near the critical angle and at
the "magnetic" peak reveals that the magnetic structure of the multilayer is
formed by two spirals, one in the odd and another one in the even iron layers,
with the opposite signs of rotation. The double-spiral structure starts from
the surface with the almost antiferromagnetic alignment of the adjacent Fe
layers. The rotation of the two spirals leads to nearly ferromagnetic alignment
of the two magnetic subsystems at some depth, where the sudden turn of the
magnetic vectors by ~180 deg (spin-flop) appears, and both spirals start to
rotate in opposite directions. The observation of this unusual double-spiral
magnetic structure suggests that the unique properties of giant
magneto-resistance devices can be further tailored using ultrathin magnetic
layers.Comment: 9 pages, 3 figure
Laser Spectroscopy of Niobium Fission Fragments: First Use of Optical Pumping in an Ion Beam Cooler Buncher
A new method of optical pumping in an ion beam cooler buncher has been developed to selectively enhance ionic metastable state populations. The technique permits the study of elements previously inaccessible to laser spectroscopy and has been applied here to the study of Nb. Model independent mean-square charge radii and nuclear moments have been studied for Nb to cover the region of the N=50 shell closure and N≈60 sudden onset of deformation. The increase in mean-square charge radius is observed to be less than that for Y, with a substantial degree of β softness observed before and after N=60
OA07.03. Randomized, double-blind, double-dummy trial of myrrh, chamomile, coffee charcoal compared to mesalazine in maintaining remission in ulcerative colitis
Gas chromatography vs. quantum cascade laser-based N<sub>2</sub>O flux measurements using a novel chamber design
Recent advances in laser spectrometry offer new opportunities to
investigate the soil–atmosphere exchange of nitrous oxide. During two field
campaigns conducted at a grassland site and a willow field, we tested the
performance of a quantum cascade laser (QCL) connected to a newly developed
automated chamber system against a conventional gas chromatography (GC)
approach using the same chambers plus an automated gas sampling unit with
septum capped vials and subsequent laboratory GC analysis. Through its high
precision and time resolution, data of the QCL system were used for
quantifying the commonly observed nonlinearity in concentration changes
during chamber deployment, making the calculation of exchange fluxes more
accurate by the application of exponential models. As expected, the curvature
values in the concentration increase was higher during long (60 min) chamber
closure times and under high-flux conditions
(FN2O > 150 µg N m−2 h−1)
than those values that were found when chambers were closed for only 10 min and/or
when fluxes were in a typical range of 2 to
50 µg N m−2 h−1. Extremely low standard errors of
fluxes, i.e., from ∼ 0.2 to 1.7 % of the flux value, were observed
regardless of linear or exponential flux calculation when using QCL data.
Thus, we recommend reducing chamber closure times to a maximum of 10 min
when a fast-response analyzer is available and this type of chamber system is
used to keep soil disturbance low and conditions around the chamber plot as
natural as possible. Further, applying linear regression to a 3 min data
window with rejecting the first 2 min after closure and a sampling time
of every 5 s proved to be sufficient for robust flux determination while ensuring
that standard errors of N2O fluxes were still on a relatively low level.
Despite low signal-to-noise ratios, GC was still found to be a useful method
to determine the mean the soil–atmosphere exchange of N2O on longer timescales
during specific campaigns. Intriguingly, the consistency between GC and
QCL-based campaign averages was better under low than under high N2O
efflux conditions, although single flux values were highly scattered during
the low efflux campaign. Furthermore, the QCL technology provides a useful
tool to accurately investigate the highly debated topic of diurnal courses
of N2O fluxes and its controlling factors. Our new chamber design
protects the measurement spot from unintended shading and minimizes
disturbance of throughfall, thereby complying with high quality requirements
of long-term observation studies and research infrastructures
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