1,308 research outputs found
Changes in the activities of ornithine transcarbarnylase and arginase, and concentrations of nitrogenous substances during germination and seedling development of Vitis vinifera L.
During germination and subsequent growth of seedlings of Vitis vinifera L. cv. Chenin blanc, marked changes occurred in the concentrations of the total nonprotein nitrogen fraction, amino nitrogen, and alnide nitrogen, and in the activities of ornithine transcarbamylase (OTC) and arginase. The level of total nonprotein nitrogen was lower in seeds than in seedlings, with maximum concentration reached at the 3rd stage of seedling growth (10 to 15 d after germination) and thereafter declining rapidly. Changes in the concentration of amino nitrogen and amide nitrogen fractions paralleled that of the total nonprotein nitrogen. The concentration of glutalnine exceeded that of asparagine at all stages of seedling development. The presence of OTC and arginase in seeds and seedlings, as well as the parallel changes between arginase activity and concentration of free arginine, suggested that the biosynthesis and degradation of this amino acid in grapevine tissues occurs through the KREBS-HENSELEIT pathway. The MICHAELIS constant for arginase, calculated from the LINEWEAVER-BURK plot, differed in seedlings at three different stages of seedling development. VerĂ€nderungen in der AktivitĂ€t der Ornithintranscarbamylase und der Arginase sowie der Konzentration der Stickstoffverbindungen wĂ€hrend der Keimung und der SĂ€mlingsentwicklung von Vitis vinifera L.Im Verlauf der Keimung und des anschlieĂenden Wachstums der SĂ€mlinge von Vitis vinifera L., cv . Chenin blanc, traten deutliche VerĂ€nderungen in der Konzentration des gesamten nicht-proteingebundenen Stickstoffs, des Amino- und des Amidstickstoffs sowie in der AktivitĂ€t der Ornithintranscarbamylase (OTC) und der Arginase auf. Die Samen besaĂen einen niedrigeren Gehalt an gesamtem nicht-proteingebundenem Stickstoff als die SĂ€mlinge, wobei die maximale Konzentration im 3. Stadium des SĂ€mlingswachstums erreicht wurd~ (10-15 d nach der Keimung); danach nahm sie rasch ab. Die Verschiebungen in der Konzentration des Amino- und Amidstickstoffs verliefen parallel zu den KonzentrationsĂ€nderungen des gesamten nichtproteingebundenen Stickstoffs. In allen Stadien der SĂ€mlingsentwicklung lag die Glutamin- ĂŒber der Asparaginkonzentration. Das Vorkommen von OTC und Arginase in Samen und SĂ€mlingen sowie die parallelen VerĂ€nderungen von ArginaseaktivitĂ€t und Konzentration des freien Arginins la~sen vermuten, daĂ die Biosynthese und der Abbau dieser AminosĂ€ure im Rebengewebe ĂŒber den KREBS-HENSELEIT-Cyklus ablaufen. In den SĂ€mlingsstadien 3, 4 und 5 wurden - nach LINEWEAVER-BURK - unterschiedliche MICHAELIS Konstanten der Arginase ermittelt
Ammonia assimilation in Vitis vinifera L.: II. Leaf and root glutamine synthetase
Glutamine synthetase (GS) activity in Vitis vinifera L. cv. Chenin blanc leaf and root tissues was present in the supernatant and particulate fractions. The percentage distribution of GS activity in leaf and root extracts were respectively 39.5 and 49.2 % in the 10,000 gpellet, 38.6 and 41.1 % in the 2.3,500 gpellet, and 21.9 and 9.7 % in the 23,500 g supernatant fractions. Leaf GS activity was always greater than root enzyme activity. Kinetic studies revealed no significant differences between leaf and root GS from the 10,000 g pellet fraction. The Km values for L-glutamate, ATP and hydroxylamine were respectively 3.2 ± 0.7 mM, 0.8 ± 0.2 mM, and 0.8 ± 0.2 mM. Formation of y-glutamyl hydroxamate was linear for the first 35 min. Optimum in vitro reaction conditions were pH 7.70-8.10, incubation temperature 37 °C, and amount of enzyme equivalent to 75-105 mg of fresh tissue. L-arginine, L-ornithine and carbamyl phosphate at a concentration of 5 mM caused inhibition of 13.6 and 12 %, respectively.Die Ammonium-Assimilation bei Vitis vinifera L.:II. Die Glutaminsynthetase der BlĂ€tter und WurzelnBei der Rebsorte Chenin blanc (Vitis vinifera L.) lag nach differenzierter Zentrifugation sowohl in den löslichen wie in den strukturierten Fraktionen Glutaminsynthetase-(GS-)AktivitĂ€t vor. Die prozentuale Verteilung der GS-AktivitĂ€t auf Blatt- und Wurzelextrakte betrug jeweils 39,5 und 49,2 % im 10 000-g-Sediment, 38,6 und 41,1 % im 23 500-g-Sediment sowie 21,9 und 9,7 % im 23 500-g-Ăberstand. In den BlĂ€ttern war die GS-AktivitĂ€t stets höher als in den Wurzeln. Untersuchungen der Enzymkinetik erbrachten bei dem 10 000-g-Sediment keine signifikanten Unterschiede zwischen der GS-AktivitĂ€t der BlĂ€tter und der Wurzeln. Die Km-Werte fĂŒr L-Glutamat, ATP und Hydroxylamin betrugen 3,2 ± 0,7 mM, 0,8 ± 0,2 mM und 0,8 ± 0,2 mM. Die Bildung von y-Glutamylhydroxamat verlief in den ersten 35 min linear. In vitro waren die optimalen Reaktionsbedingungen ein pH von 7,70-8,10, eine Inkubationstemperatur von 37 °C und eine Enzymmenge, die dem Gehalt von 75-105 mg Frischgewebe entsprach. L-Arginin, L-Ornithin und Carbamylphosphat in Konzentrationen von 5 mM hemmten die Enzymwirkung ·um 13,6 bzw. 12%
Ammonia assimilation in Vitis vinifera L.: III. Glutamate oxaloacetate transaminase from leaf and root tissue
Glutamate-oxaloacetate transaminase (GOT) activities in Vitis vinifera L. cv. Chenin blanc leaf and root tissues were associated only with the soluble fraction. Mean in vitro enzyme activity of both tissues was 4.3 ± 0.8 ÎŒmol oxaloacetate formed per g fresh tissue per hour. Km values of GOT from leaves and roots were (1.9 ± 0.4) · 10-4 M for α-ketoglutarate and (4.7 ± 0.5) · 10-3 M for L-aspartate. Optimum in vitro conditions for GOT activity were pH 7.4-7.8, amount of enzyme equivalent to 95-130 mg fresh tissue and incubation temperature 38-39 °C. Neither leaf nor root GOT responded to exogenous pyridoxal-5' phosphate.Die Ammonium-Assimilation bei Vitis vinifera L.:III. GlutamatcOxalacetat-Transaminase aus Blatt- und WurzelgewebeDie AktivitĂ€t der Glutamat-Oxalacetat-Transaminase (GOT) in Blatt- und Wurzelgewebe der Rebsorte Chenin blanc (Vitis vinifera L.) war auf die lösliche Fraktion beschrĂ€nkt. In vitro betrug die mittlere EnzymaktivitĂ€t in beiden Organen 4,3 ± 0,8 ÎŒmol Oxalacetat je g Frischgewicht und h. Die Km-Werte von GOT aus BlĂ€ttern und Wurzeln betrugen (1,9±0,4) . 10-4 M fĂŒr α-Ketoglutarat und (4,7±0,5) · 10-3 M fĂŒr L-Aspartat. Die optimalen Bedingungen der GOT-AktivitĂ€t waren in vitro ein pH von 7,4-7,8, eine Enzymmenge, die dem Gehalt von 95-130 mg Frischmaterial entsprach, und eine Inkubationstemperatur von 38-39 °C. Weder Blatt- noch Wurzel-GOT reagierten auf zugesetztes Pyridoxal-5'-Phosphat
Ammonia assimilation in Vitis vinifera L.: I. Isolation and properties of leaf and root glutamate dehydrogenase
Glutamate dehydrogenase (GDH) activity in Vitis vinifera L. cv. Chenin blanc leaf and root tissues was associated with the particulate and the soluble fractions. In leaf extracts, about 66 % of the NADH-GDH activity was in the 10,000 g pellet and about 34 % was in the 23,500 gpellet fractions, whereas NADPH-GDH activity was associated mainly with the soluble fraction (23,500 g). In root extracts, about 53 % of the NADHGDH activity was in the soluble and 43 % in the 10,000 gpellet fractions, whereas about 47, 37, and 16 % of NADPH-GDH activity were in the soluble, 10,000 g and 23,500 gpellet fractions, respectively. GDH from the 10,000 gpellet of leaf and the soluble fraction of root extracts differed in their affinities to substrates. The Km values of leaf and root GDH were, respectively, 3.9 ± 1.1 and 0.7 ± 0.4 mM for a-ketoglutarate; 35.7 ± 7.1 and 61.3 ± 12.4 mM for NH4Cl; and 100.0 ± 7.4 and 36.2 ± 4.4 ÎŒM for NADH. GDH from leaf and root tissues showed Michaelis-Meuten kinetics with all. substrates except NH4Cl, which exhibited a sigmoid relationship in roots. Optimum in vitro reaction conditions were pH 7.90-8.10, incubation temperature of 38-40 °C, and amount of enzyme equivalent to 80-110 mg of fresh tissue. Enzyme from both leaves and roots was inhibited by EDTA and L-glutamate. Activation with Ca2+ was more pronounced in root GDH than in leaf GDH.Die Ammonium-Assimilation bei Vitis vinifera L.:1. Isolierung und Eigenschaften der Glutamatdehydrogenase aus BlĂ€ttern und WurzelnBei der Rebsorte Chenin blanc (Vitis vinifera L.) wurde die Glutamatdehydrogenase- (GDH-)AktivitĂ€t der strukturierten und löslichen Fraktionen von Blattund Wurzelgeweben bestimmt. Die NADH-GDH-AktivitĂ€t von Blattextrakten verteilte sich zu ca. 66 % auf das nach Zentrifugation bei 10 000 g erhaltene Sediment und zu ca. 34 % auf das 23 500-g Sediment, wĂ€hrend die NADPH-GDH-AktivitĂ€t hauptsĂ€chlich an die lösliche Fraktion (23 500 g) gebunden war. Bei Wurzelextrakten waren ca. 53 % der NADH-GDH-AktivitĂ€t in der löslichen Fraktion und 43 % im 10 000-g-Sediment enthalten, wĂ€hrend jeweils 47, 37 und 16 % der NADPHGDH- AktivitĂ€t auf die lösliche Fraktion, das 10 000-g-Sediment bzw. das 23 500-g-Sediment entfielen. Die GDH aus dem 10 000-g-Sediment des Blattmaterials und aus der löslichen Fraktion der Wurzelextrakte unterschieden sich in ihrer SubstrataffinitĂ€t. Die Km-Werte der Blatt- und Wurzel GDH betrugen 3,9 ± 1,1 bzw. 0,7 ± 0,4 mM fĂŒr a-Ketoglutarat, 35,7 ± 7,1 bzw. 61,3 ± 12,4 mM fĂŒr NH4Cl sowie 100,0 ± 7,4 bzw. 36,2 ± 4,4 ÎŒM fĂŒr NADH. Die GDH aus Blatt- und Wurzelgeweben folgte mit allen Substraten der Michaelis-Menten-Kinetik, ausgenommen mit NH4Cl; hier lag bei Wurzelextrakten eine sigmoide Beziehung vor. In vitro waren die optimalen Reaktionsbedingungen ein pH von 7,90-8,10, eine Inkubationstemperatur von 38-40 °C und eine Enzymmenge, die dem Gehalt von 80-110 mg Frischgewebe entsprach. Durch EDTA und L-Glutamat wurde das Enzym sowohl der BlĂ€tter als auch der Wurzeln inhibiert. Wurzel-GDH wurde durch Ca2+ stĂ€rker aktiviert als Blatt-GDH
Focussing quantum states
Does the size of atoms present a lower limit to the size of electronic
structures that can be fabricated in solids? This limit can be overcome by
using devices that exploit quantum mechanical scattering of electron waves at
atoms arranged in focussing geometries on selected surfaces. Calculations
reveal that features smaller than a hydrogen atom can be obtained. These
structures are potentially useful for device applications and offer a route to
the fabrication of ultrafine and well defined tips for scanning tunneling
microscopy.Comment: 4 pages, 4 figure
Lifetimes of electrons in the Shockley surface state band of Ag(111)
We present a theoretical many-body analysis of the electron-electron (e-e)
inelastic damping rate of electron-like excitations in the Shockley
surface state band of Ag(111). It takes into account ab-initio band structures
for both bulk and surface states. is found to increase more rapidly as
a function of surface state energy E than previously reported, thus leading to
an improved agreement with experimental data
Model study of adsorbed metallic quantum dots: Na on Cu(111)
We model electronic properties of the second monolayer Na adatom islands
(quantum dots) on the Cu(111) surface covered homogeneously by the first Na
monolayer. An axially-symmetric three-dimensional jellium model, taking into
account the effects due to the first Na monolayer and the Cu substrate, has
been developed. The electronic structure is solved within the local-density
approximation of the density-functional theory using a real-space multigrid
method. The model enables the study of systems consisting of thousands of
Na-atoms. The results for the local density of states are compared with
differential conductance () spectra and constant current topographs from
Scanning Tunneling Microscopy.Comment: 10 pages, 8 figures. For better quality figures, download
http://www.fyslab.hut.fi/~tto/cylart1.pd
Role of elastic scattering in electron dynamics at ordered alkali overlayers on Cu(111)
Scanning tunneling spectroscopy of p(2x2) Cs and Na ordered overlayers on
Cu(111) reveals similar line widths of quasi two-dimensional quantum well
states despite largely different binding energies. Detailed calculations show
that 50% of the line widths are due to electron-phonon scattering while
inelastic electron-electron scattering is negligible. A frequently ignored
mechanism for ordered structures, i.e., enhanced elastic scattering due to
Brillouin zone back folding, contributes the remaining width.Comment: 4 pages, 2 figures, 1 tabl
Interaction of the Electromagnetic p-Waves with Thin Metal Films
For the first time it is shown that for thin metallic films thickness of
which not exceed thickness of skin-layer, the problem allows analytical
solution for arbitrary boundary value problems. The analysis of dependence of
coefficients of transmission, reflection and absorbtion on angle incidence,
thickness of films and coefficient of specular reflection is carried out.Comment: 15 pages, 9 figure
Statistical mechanical aspects of joint source-channel coding
An MN-Gallager Code over Galois fields, , based on the Dynamical Block
Posterior probabilities (DBP) for messages with a given set of autocorrelations
is presented with the following main results: (a) for a binary symmetric
channel the threshold, , is extrapolated for infinite messages using the
scaling relation for the median convergence time, ;
(b) a degradation in the threshold is observed as the correlations are
enhanced; (c) for a given set of autocorrelations the performance is enhanced
as is increased; (d) the efficiency of the DBP joint source-channel coding
is slightly better than the standard gzip compression method; (e) for a given
entropy, the performance of the DBP algorithm is a function of the decay of the
correlation function over large distances.Comment: 6 page
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