Developmental control of N-CAM sialylation state by Golgi sialyltransferase isoforms

Development ◽  
1988 ◽  
Vol 104 (1) ◽  
pp. 147-154 ◽  
Author(s):  
K.C. Breen ◽  
C.M. Regan
Keyword(s):  
Enzyme Assay ◽  
Specific Activity ◽  
Solid Phase ◽  
Competitive Inhibitor ◽  
Temporal Expression ◽  
Ferric Ions ◽  
Developmentally Regulated ◽  
Sialyltransferase Activity ◽  
The Individual ◽  
Kinetics Of

A rat brain Golgi sialyltransferase activity capable of the differentiation-dependent control of N-CAM sialylation state is described. The specific activity of Golgi sialyltransferase was found to be developmentally regulated with respect to both endogenous and exogenous protein acceptors, with a particular elevation on postnatal days 10–12 when the heavily sialylated or ‘embryonic’ form of N-CAM is re-expressed. The subsequent developmental decrease in activity was associated with a significant decrease in apparent Km for the CMP-NeuNAc substrate, but not for the asialofetuin exogenous acceptor, which could not be attributed to the temporal expression of an endogenous competitive inhibitor. The apparent Vmax remained constant for CMP-NeuNAc but was significantly reduced for asialofetuin. Sialyltransferase activity, which was optimal at pH 7.0-7.5, was also modulated by various cations. Zinc abolished enzyme function, in contrast to ferric ions which stimulated activity fourfold-sevenfold. The marked activation of the adult form of the enzyme by potassium and magnesium ions, together with the alterations in kinetic constants, suggested this activity to be distinct from that derived from postnatal day-12 tissue. The kinetics of [14C]sialic acid incorporation into immuno-precipitated N-CAM demonstrated the individual polypeptides to be sialylated, possibly by addition of polysialosyl units, in a developmental sequence. The presence of four distinct sialyltransferase activities was demonstrated by non-denaturing gel electrophoresis followed by solid-phase enzyme assay. These isoforms were temporally expressed during development, two being correlated with the postnatal reexpression of the ‘embryonic’ form of N-CAM.

where K = kelvin. Because of the low temperature elevation in the low dose range, radiation calorimetry is limited in practice to the dose range above 3 kGy. This small temperature elevation is the gross result of the complex process of radiation interaction with matter. The individual steps of this process depend on the type of radiation used. Another type of physical dose meter, one that is used more and more in research and in industrial practice, is the alanine/electron spin resonance (ESR) system. Stable free radicals produced by irradiation in a concentration propor­ tional to the radiation dose in samples of pure, dry alanine are measured by ESR spectroscopy. The alanine is usually mixed 4:1 with paraffin (26) or 1:1 with polystyrene (27) of analytical grade quality. Reproducible dose response curves are obtained in the extremely wide dose range of 1 Gy to 100 kGy. In principal, any reproducible change caused by irradiation of a medium can be used to measure the absorbed radiation dose. In practice, only those changes can be evaluated which are stable for a reasonable length of time and which can be reliably measured by standard procedures such as titration or spectrophotometry. The chemical change is usually expressed as the G value, which is a measure of the number of atoms, molecules, or ions produced ( + G) or destroyed ( -G ) by 100 eV of absorbed energy. In the new SI system of units the G value is expressed as per J instead of per 100 eV. An important reference dose meter in food irradiation is the ferrous sulfate or Fricke dose meter. It is based on the radiation-induced oxidation of ferrous ions (Fe + ) to ferric ions (Fe + ) and consists of measuring the increased optical absorbance of the ferric ions at the absorption peak of 305 nm. For 60Co gamma rays the G value for ferric ion yield is 15.6 Fe3+ ions per 100 eV, or 9.74 X 1017 ions/J; the yield for electrons at a dose rate of 108 Gy/sec is 13.0. Fricke dosimetry is useful in the range 3 Gy. The upper limit can be extended into the kGy range by adding CuS04, which reduces the G value from 15.6 to 0.65. There are many other systems, such as the ethanol-chlorobenzene dose meter, which is based on the formation of hydrochloric acid from chlorobenzene. The hydrochloric acid can be measured by titration or by its effect on the dielectric constant. The useful dose range of this system is 1-400 Gy. In the low dose range, down to 5 Gy, radiochromic dye dosimetry can be used. When the colorless solution of pararosaniline cyanide in 2-methoxyethanol and glacial acetic acid is irradiated, an intense red color develops with an absorption maximum at 549 nm. More recently proposed methods belonging to the group of liquid dose meter systems are listed in Table 3. PMA (polymethyl methacrylate) dose meters belong to the group of solid phase dose meters. Irradiation of PMMA (e.g., Perspex) induces an absorption

1995 ◽  
pp. 50-50
Keyword(s):  
Hydrochloric Acid ◽  
Radiation Dose ◽  
Low Dose ◽  
Solid Phase ◽  
Dose Range ◽  
Chemical Change ◽  
Temperature Elevation ◽  
Ferric Ions ◽  
G Value ◽  
The Individual

scholarly journals 8-vinyl reduction and chlorophyll a biosynthesis in higher plants

1993 ◽  
Vol 291 (3) ◽  
pp. 939-944 ◽  
Author(s):  
B J Whyte ◽  
W T Griffiths
Keyword(s):  
Triticum Aestivum ◽  
Chlorophyll A ◽  
Redox State ◽  
Higher Plants ◽  
Solid Phase ◽  
Compositional Analysis ◽  
The Individual ◽  
Vinyl Reductase ◽  
Kinetics Of ◽  
Chlorophyll A Biosynthesis

A technique involving solid-phase extractions and polyethylene h.p.l.c. suitable for the routine compositional analysis of the total protochlorophyllide pool of plants is described. The resynthesis kinetics of the individual components of the pool have been studied in briefly illuminated etiolated tissue of wheat (Triticum aestivum) and cucumber (Cucumis sativus) during subsequent redarkening. The data are interpreted in terms of a precursor-product relationship between the di- and mono-vinyl analogues of protochlorophyllide during their reaccumulation in darkness. The interconversion is assumed to be catalysed by an 8-vinyl reductase, which shows greater activity in wheat than in cucumber. Analyses of the redox state of the nicotinamide nucleotide of the pool during the process are compatible with NADPH as the cofactor of the putative reductase.

Kinetic Aspects of the Interaction of Blood Clotting Enzymes

1968 ◽  
Vol 19 (03/04) ◽  
pp. 364-367 ◽  
Author(s):  
H. C Hemker ◽  
P. W Hemker
Keyword(s):  
Enzyme Kinetics ◽  
Blood Clotting ◽  
Competitive Inhibition ◽  
Competitive Inhibitor ◽  
Kinetics Of

SummaryThe enzyme kinetics of competitive inhibition under conditions prevailing in clotting tests are developed and a method is given to measure relative amounts of a competitive inhibitor by means of the t — D plot.

The role of secondary alcoholic groups of D-galacturonan in its degradation with exo-D-galacturonanase

1980 ◽  
Vol 45 (2) ◽  
pp. 427-434 ◽  
Author(s):  
Kveta Heinrichová ◽  
Rudolf Kohn
Keyword(s):  
Acetyl Derivative ◽  
Competitive Inhibitor ◽  
Hydroxyl Groups ◽  
Pectic Acid ◽  
Substrate Complex ◽  
Enzyme Substrate ◽  
The Individual ◽  
Degradation Degree ◽  
Derivatives Of

The effect of exo-D-galacturonanase from carrot on O-acetyl derivatives of pectic acid of variousacetylation degree was studied. Substitution of hydroxyl groups at C(2) and C(3) of D-galactopyranuronic acid units influences the initial rate of degradation, degree of degradation and its maximum rate, the differences being found also in the time of limit degradations of the individual O-acetyl derivatives. Value of the apparent Michaelis constant increases with increase of substitution and value of Vmax changes. O-Acetyl derivatives act as a competitive inhibitor of degradation of D-galacturonan. The extent of the inhibition effect depends on the degree of substitution. The only product of enzymic reaction is D-galactopyranuronic acid, what indicates that no degradation of the terminal substituted unit of O-acetyl derivative of pectic acid takes place. Substitution of hydroxyl groups influences the affinity of the enzyme towards the modified substrate. The results let us presume that hydroxyl groups at C(2) and C(3) of galacturonic unit of pectic acid are essential for formation of the enzyme-substrate complex.

Kinetics and Mechanism of Decomposition of 1,3-Bis(4-methylphenyl)triazene Catalyzed with Substituted Benzoic Acids in 25% Aqueous Methanol-General or Specific Catalysis?

1994 ◽  
Vol 59 (9) ◽  
pp. 2029-2041
Author(s):  
Oldřich Pytela ◽  
Taťjana Nevěčná
Keyword(s):  
Benzoic Acids ◽  
Hammett Equation ◽  
Aqueous Methanol ◽  
Mechanism Of Decomposition ◽  
Kinetics Of Decomposition ◽  
Independent Variable ◽  
Amino Derivatives ◽  
Substituted Benzoic Acids ◽  
The Individual ◽  
Kinetics Of

The kinetics of decomposition of 1,3-bis(4-methylphenyl)triazene catalyzed with 13 substituted benzoic acids of various concentrations have been measured in 25 vol.% aqueous methanol at 25.0 °C. The rate constants observed (297 data) have be used as values of independent variable in a series of models of the catalyzed decomposition. For the catalytic particles were considered the undissociated acid, its conjugated base, and the proton in both the specific and general catalyses. Some models presumed formation of reactive or nonreactive complexes of the individual reactants. The substituent effect is described by the Hammett equation. The statistically best model in which the observed rate constant is a superposition of a term describing the dependence on proton concentration and a term describing the dependence on the product of concentrations of proton and conjugated base is valid with the presumption of complete proton transfer from the catalyst acid to substrate, which has been proved. The behaviour of 4-dimethylamino, 4-amino, and 3-amino derivatives is anomalous (lower catalytic activity as compared with benzoic acid). This supports the presumed participation of conjugated base in the title process.

Kinetics of esterification of monoisopropylphenols with phosphoryl trichloride

1989 ◽  
Vol 54 (5) ◽  
pp. 1311-1317
Author(s):  
Miroslav Magura ◽  
Ján Vojtko ◽  
Ján Ilavský
Keyword(s):  
Liquid Phase ◽  
Rate Constants ◽  
Reaction Rates ◽  
Activation Energies ◽  
The Individual ◽  
Kinetics Of

The kinetics of liquid-phase isothermal esterification of POCl3 with 2-isopropylphenol and 4-isopropylphenol have been studied within the temperature intervals of 110 to 130 and 90 to 110 °C, respectively. The rate constants and activation energies of the individual steps of this three-step reaction have been calculated from the values measured. The reaction rates of the two isomers markedly differ: at 110 °C 4-isopropylphenol reacts faster by the factors of about 7 and 20 for k1 and k3, respectively. This finding can be utilized in preparation of mixed triaryl phosphates, since the alkylation mixture after reaction of phenol with propene contains an excess of 2-isopropylphenol over 4-isopropylphenol.

Fully Automated Parallel Oligonucleotide Synthesizer

2001 ◽  
Vol 66 (8) ◽  
pp. 1299-1314 ◽  
Author(s):  
Michal Lebl ◽  
Christine Burger ◽  
Brett Ellman ◽  
David Heiner ◽  
Georges Ibrahim ◽  
...  
Keyword(s):  
Solid Phase ◽  
Building Blocks ◽  
Solid Support ◽  
Continuous Operation ◽  
Gear Pump ◽  
Oligonucleotide Synthesis ◽  
Center Of Rotation ◽  
Microtiter Plates ◽  
The Individual ◽  
Design And Construction

Design and construction of automated synthesizers using the tilted plate centrifugation technology is described. Wash solutions and reagents common to all synthesized species are delivered automatically through a 96-channel distributor connected to a gear pump through two four-port selector valves. Building blocks and other specific reagents are delivered automatically through banks of solenoid valves, positioned over the individual wells of the microtiterplate. These instruments have the following capabilities: Parallel solid-phase oligonucleotide synthesis in the wells of polypropylene microtiter plates, which are slightly tilted down towards the center of rotation, thus generating a pocket in each well, in which the solid support is collected during centrifugation, while the liquid is expelled from the wells. Eight microtiterplates are processed simultaneously, providing thus a synthesizer with a capacity of 768 parallel syntheses. The instruments are capable of unattended continuous operation, providing thus a capacity of over two millions 20-mer oligonucleotides in a year.

scholarly journals A Study of the Impact of Graphite on the Kinetics of SPS in Nano- and Submicron WC-10%Co Powder Compositions

Ceramics ◽  
2021 ◽  
Vol 4 (2) ◽  
pp. 331-363
Author(s):  
Eugeniy Lantcev ◽  
Aleksey Nokhrin ◽  
Nataliya Malekhonova ◽  
Maksim Boldin ◽  
Vladimir Chuvil'deev ◽  
...  
Keyword(s):  
Activation Energy ◽  
Solid Phase ◽  
Continuous Heating ◽  
Diffusion Creep ◽  
Hard Alloys ◽  
Fine Grained ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
The Impact ◽  
Kinetics Of

This study investigates the impact of carbon on the kinetics of the spark plasma sintering (SPS) of nano- and submicron powders WC-10wt.%Co. Carbon, in the form of graphite, was introduced into powders by mixing. The activation energy of solid-phase sintering was determined for the conditions of isothermal and continuous heating. It has been demonstrated that increasing the carbon content leads to a decrease in the fraction of η-phase particles and a shift of the shrinkage curve towards lower heating temperatures. It has been established that increasing the graphite content in nano- and submicron powders has no significant effect on the SPS activation energy for “mid-range” heating temperatures, QS(I). The value of QS(I) is close to the activation energy of grain-boundary diffusion in cobalt. It has been demonstrated that increasing the content of graphite leads to a significant decrease in the SPS activation energy, QS(II), for “higher-range” heating temperatures due to lower concentration of tungsten atoms in cobalt-based γ-phase. It has been established that the sintering kinetics of fine-grained WC-Co hard alloys is limited by the intensity of diffusion creep of cobalt (Coble creep).

Effect of maturity of Napier grass (Pennisetum purpureum) hay on intake, digestibility, and rumen dynamics when given to zebu bulls

2000 ◽  
Vol 2000 ◽  
pp. 144-144
Author(s):  
A.J. Ayala-Burgos ◽  
F.D.DeB. Hovell ◽  
R.M. Godoy ◽  
Hamana S. Saidén ◽  
R. López ◽  
...  
Keyword(s):  
Liquid Phase ◽  
Solid Phase ◽  
Napier Grass ◽  
Pennisetum Purpureum ◽  
Ad Libitum ◽  
The Tropics ◽  
Kinetics Of

Cattle in the tropics mostly depend on pastures. During dry periods the forage available is usually mature, constraining both intake and digestion. These constraints need to be understood, for intake and digestibility define productivity. Intake depends on the rumen space made available by fermentation and outflow. Markers such as PEG (liquid phase), and chromium mordanted fibre (solid phase) can be used to measure rumen volume and outflow, but have limitations. The objective of this experiment was to measure intake, digestibility, and rumen kinetics of cattle fed ad libitum forages with very different degradation characteristics, and also to compare rumen volumes measured with markers with those obtained by manual emptying.

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