共查询到20条相似文献,搜索用时 15 毫秒
1.
Methyl 2-deoxy-3,5,6-tri- O-p-nitrobenzoyl-
- ribo-hexofuranoside was converted into the glycosyl halide which was then condensed with 2,4-bis(trimethylsilyloxy)-pyrimidine in the presence of mercuric chloride to give, after alkaline methanolysis, 1-(2-deoxy-β-
- ribo-hexofuranosyl)uracil, in a yield too low for the reaction to be applied to deuterated compounds. Methyl 2-deoxy-
-allofuranoside-2- d was degraded into methyl 2-deoxy-
-arabinofuranoside-2- d. Its di- p-nitrobenzoate was converted into the glycosyl halide which was coupled with 2,4-bis(trimethylsilyloxy)-pyrimidine to give, after alkaline hydrolysis, deuterated deoxyuridine. Thiationammonolysis of a mixture of the 3′,5′-di- p-nitrobenzoates of the latter compound and its anomer gave the corresponding deoxycytidines. Comparison of the n.m.r. spectra of these compounds to that of deuterated deoxycytidine, prepared by the enzymic reduction of cytidine 5′-pyrophosphate with the Escherichia coli system in the presence of deuterium oxide confirmed that the substitution of a hydroxyl group by a hydrogen atom proceeds with retention of configuration. 相似文献
3.
Commercial aqueous 25 per cent glutaraldehyde solutions contain no stable derivative of this aldehyde, but compounds of variable molecular weight which easily revert to glutaraldehyde. The effect of pH on the reaction of glutaraldehyde with amino acids and on the stability of the products under acid conditions, shows the importance of the structure modification of the dialdehyde which occurs when pH increases, and even leads to precipitation in highly alkaline solutions. This precipitate results from aldol condensation of glutaraldehyde molecules. It contains aldehyd groups conjugated with ethylenic double bonds. Such a structure reacts with amino groups to give an imino bond, stabilized by resonance with the ethylenic bond, and does not undergo Michael-type addition reactions.Therefore, glutaraldehyde does not react with proteins under its free form, but as an unsaturated polymer, which gives imino bonds stabilized by conjugation. 相似文献
4.
1. A glycoprotein: fucosyl-transferase activity was demonstrated in sheep cerebral cortex, using desialylated fetuin as exogenous acceptor and detergent Trition X 100 for solubilization. 2. Addition of Triton X 100 to the membrane suspension gave first an activation then a solubilization of the cerebral fucosyl-transferase. 3. Hydrophobic chromatography was investigated for purification of the enzyme. Binding was effective using alkyl-agarose chromatographic columns with two or more than two atoms of carbon, but elution was only possible with ethyl and butyl-agarose. 4. Combination of subcellular fractionation and hydrophobic chromatography on ethylagarose led to a 30 fold purification. 5. After ethyl-agarose chromatography, some properties of fucosyl-transferase were studied: the optimal temperature was 25°C. The optimum pH was about neutrality. Light activation was observed with Mn2+ concentration below 1 mM. 6. Homogeneity was tested using Ultrogel chromatography, polyacrylamide gel electrophoresis and ultracentrifugation. 7. It was concluded that ethyl-agarose hydrophobic chromatography easily bind a few solubilized proteins (about 20 per cent of the ST supernatant). When elution was performed, these proteins, including fucosyl-transferase, were released from ethyl-agarose columns as a stable aggregate, only dissociated with lower ionic strength. Ethyl-agarose fraction (eluted with KCl 120 mM) showed homogeneity: — with Ultrogel AcA 22 chromatography (Mw = 300.000). — with polyacrylamide gel electrophoresis without S.D.S. — with the analytical ultracentrifugo giving Mw = 280.000; S20 = 10. But after dialysis overnight against a buffer without KCl, ultracentrifugation technics showed no homogeneity. Futhermore, SDS gel electrophoresis gave more than four bands. 相似文献
5.
Degradation of Amino Acids at a Simulated Water-sediment Interface of a Mediterranean Lagoon Environment, Golfe du Lion The degradation of two 14C and 3H labelled amino acids at the simulated water-sediment interface of a Mediterranean lagoon was studied. The four day experiments included the respiratory activity measurement and the study of incorporation processes of the radioactivity in specific organic fractions of the 14C arginine. After active mineralization occurred during the first day, the radioactivity in the acid-soluble fraction decreased and polycondensed products were progressively incorporated. The radioactivity of the 3H lysine was included mainly in the acid soluble fraction. The nature of the substrate, and the reducing conditions in the environment affect the radioactivity distribution in the organic fractions. The identification of amino acids in the acid-soluble and base soluble fractions shows that the labelled arginine and lysine and other amino acids in the acid soluble and base soluble fractions shows that the labelled arginine and lysine released from the initial compounds are important quantitatively. 相似文献
7.
Pure rabbit fibrinogen was prepared by a method involving two ammonium sulfate precipitations, one 2 M phosphate buffer precipitation, one DEAE cellulose chromatography and lastly one Sepharose 6 B chromatography. The aminoacid composition was determined and an immunonephelemetric assay was proposed. This assay allowed an accurate determination of fibrinogen concentration in a rabbit with inflammatory reaction. 相似文献
9.
The Comparative Productivity of Two Ponds in the Vicinity of Lake St-John, Québec In 1980 and 1981, the productivity of two ponds near Lake St. John were evaluated. One, the pond of Desbiens, did not communicate with Lake St. John and the other, the pond of St-Gédéon, was connected to the lake. The aim of this study was to evaluate the contribution that a pond could make to the increase in productivity of Lake St. John which is a reservoir. The pond of Desbiens is more productive than Lake St. John but two to three times less than the pond of St-Gédéon. The pond of Desbiens shows an advanced degree of eutrophication whereas the pond of St-Gédéon is similar to the northern lakes by its physico-chemistry, zooplankton, sediments and benthic fauna. If we want to create artificial ponds, for a better productivity of reservoirs, it is important that they be connected to each other. 相似文献
10.
Sibling species groups are suitable models for the understanding of inter‐ and intraspecific processes in taxonomy and biogeography. We analysed 262 individuals from the Alps of the Coenonympha arcania/gardetta species complex by allozyme electrophoresis. These taxa showed high variance amongst populations ( FST: 0.391) and strong intertaxon genetic differentiation ( FCT: 0.376). Although morphologically similar, Coenonympha gardetta and Coenonympha arcania clearly differ in their genetic characteristics; the morphologically intermediate taxa Coenonympha darwiniana darwiniana and Coenonympha darwiniana macromma are genetically well distinguished from each other and the two other taxa. Coenonympha arcania and C. d. macromma most probably share a common ancestor and evolved by cladogenesis, whereas the taxonomic situation of C. d. darwiniana is still unresolved: This taxon might be the result of hybridization between C. arcania and C. gardetta or it might have a common ancestor together with C. gardetta. We suggest species rank for all four taxa. The distribution of genetic diversity of these populations and the differentiation amongst populations suggest rather different biogeographical scenarios: C. arcania most probably is of Mediterranean origin with postglacial range expansion northwards; C. gardetta survived the last ice age in peripheral refugia of the Alps and has spread all over this high mountain system in the postglacial; C. darwiniana and C. macromma survived the Würm in geographic proximity to their actual distribution areas and only have performed moderate uphill translocations during postglacial warming. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159 , 890–904. 相似文献
12.
Modes of aggregation fo alanine-, norvaline- and valine-contaiing dpepetides with the general formula R 1? C 1O 1? N 2H 2? CHR 2? C 2O 2? N 3H 3? R 3 have been studied in CCl 4 solution by using infrared and nuclear magnetic resonance spectroscopies. Solutions of the pure L isomer and of the racemic mixture do not give identical data. At a given concentration, the racemic mixtrue is more aggregated than the pure enantiomer, and the difference, negligible in the case of alanine derivative, increases wiht the bulkiness of the side cahin R 2. The results show that a selective interaction takes place between enantiomeric molecules, resulting ina dimer associating tow inverse configurated C 5 conformers. The stabilizaion of this dimer proceeds from two symmetrical and intermolecular H 3 … O 1 hydrogen bondings. 相似文献
16.
The statistical analysis ( Q mode) of the microfauna of 135 bottom and core samples from the Mediterranean provides evidence of the predominating local conditions in each of the two basins. Temperature, which plays a primary role in the distribution of foraminiferal species, only takes second place when one considers the regrouping of the layers. Once the temperature factor is identified, its variations provide a precise climatic curve with the advantage of not having to make any subjective interpretation of the assemblages. RésuméL'analyse en mode Q des microfaunes de 135 échantillons de Méditerrannée (niveaux de surface et carottages) met en évidence la prédominance des conditions locales propres à chacun des deux bassins. La température, qui joue un rôle primordial dans la répartition des espèces de Foraminifères, n'intervient qu'en second lieu lorsqu'on considère les regroupements des niveaux. Une fois le facteur thermique identifié, ses variations fournissent une courbe climatique précise qui présente l'avantage de ne nécessiter aucune interprétation subjective des assemblages. 相似文献
17.
The acetolysis with anhydrous acetic acid of the diazoketone 1, prepared from potassium 1,2:3,4-di- O-isopropylidene-α-D-galacturonate, gave ketoacetates having the D- glycero ( 3)and L- glycero ( 5)configuration at C-7, together with the 3-oxetanone 7, a product of pyranose-ring opening. Starting from the ketoacetates 3 and 5, the lincosamine derivative, 6-acetamido-6,8-dideoxy-1,2:,4-di- O-isopropylidene -α-D- erythro-D- galacto-octopyranose ( 8), and its three diastereoisomers at C-6 and C-7 ( 9, 10, and 11) were obtained by oximation, reduction, and N-acetylation. RésuméL'acétolyse par l'acide acétique anhydre de la diazocétone 1 dérivée du 1,2:3,4-di- O-isopropylidéne-α-D-galacturonate de potassium, donne les céto-acétates deconfiguration D- glycéro ( 3) et L- glycéro ( 5) sur C-7, ainsi que la 3-oxétanone 7 qui résulte de l'ouverture du cycle pyranosique. A partir des céto-acétates 3 et 5, on a obtenu, par oximation, réduction et N-acétylation, le dérivé de la lincosamine, 6-acétamido-6,8-didésoxy-1,2:3,4-di- O-isopropylidéne-α-D- érythro-D- galacto-octo-pyranose ( 8), et ses trois diastéréoisoméres en C-6 et C-7 ( 9, 10 et 11). 相似文献
20.
Glycerol specifically deuterated at C-1, C-2, or C-3 was prepared and used for the biosynthesis of bacterial cellulose with Acetobacter xylinum.The material obtained were converted into glucitol hexaacetate and analyzed by 250-MHz nuclear magnetic resonance and mass spectrometry. The spectra indicated that the protons of the C-3 position of the starting glycerol were incorporated as substituents of the C-6 and C-1 positions of the cellulose. Similarly, protons of the C-2 and C-5 positions of the cellulose came essentially from water and the protons bonded at the C-3 and C-4 positions of the cellulose from protons bonded to C-1 of the starting glycerol. 相似文献
|