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1.
Acyclic trans-2,3-unsaturated aldoheptonate derivatives (1–9) obtained from -aldopentoses by Witting chain-extension served as dienophiles for a detailed comparative study of their asymmetric Diels-Alder cycloaddition with cyclopentadiene. Cycloaddition under uncatalyzed thermal conditions gave mixtures of the four possible stereoisomeric norbornene adducts. The endo:exo ratios and the diastereofacial selectivities in the formation of the adducts were determined by NMR spectroscopy and by chemical transformations. The quantitative distribution of adducts as a function of stereochemistry of the dienophile is discussed.  相似文献   

2.
Seven-carbon (7-C) sugars and sugar alcohols are common in higher plants, algae, fungi and bacteria. The biochemical origin and physiological function of these monosaccharides in plants and algae however is not well understood and has not been fully investigated. Here the occurrence, metabolism, and transport of heptuloses, heptitols, and heptoses are integrated in accordance with function to emphasise the importance of these apparently neglected sugars. This therefore is the first comprehensive synthesis of knowledge about 7-C sugar biochemistry, a relatively underexplored area of carbohydrate biology that needs to be integrated into mainstream sugar research. Available information on the metabolism of heptuloses, heptitols, and heptoses in Medicago sativa (alfalfa), Persea americana (avocado), Primula sp., Kalanchoë pinnata, and the red alga Porphyridium sp. was thoroughly investigated and evaluated. Results indicate that 7-C sugars share a common precursor and are products of a TKT-dependent heptulose shunt in which Suc-derived Fru 6-P is converted either to Sed 7-P or mannoheptulose 7-P or both in competent tissues and species. In plants, free heptuloses probably arise as a consequence of phosphatase activity, whereas heptoses appear to be formed by isomerisation of the corresponding phloem translocated heptuloses following import into non-photosynthetic tissue. It is proposed that the major physiological function of 7-C sugars and heptitols, in addition to serving as a carbon sink, involves metal ion chelation, translocation and remobilisation to fulfil nutrient requirements essential for growth and development.  相似文献   

3.
4.
The couplings of N-protected amino acid esters with amino acid amides proved to be carried out in anhydrous acetonitrile in the presence of Bacillus licheniformis protease (subtilisin Carlsberg) immobilized on Celite. The maximal peptide yields were obtained with the immobilized enzyme prepared through lyophilization from a pH 10.7 buffer solution. A series of dipeptide syntheses and several segment condensations were achieved generally in high yields by the combined use of the immobilized enzyme prepared from this pH and the carbamoylmethyl ester as the acyl donor.  相似文献   

5.
The mobilization of arsenic from fern-rhizobium to frond-bacteria in As-contaminated abandoned mine environments was found to be induced by the ars gene. Uncultured Acinetobacter sp. strain MRI67 (DQ539027) and uncultured Buttiaxella sp. strain MRI-65 (DQ539024) were identified in the root/rhizosphere based on the presence of the ars gene. The arsenite-oxidizing bacterial strains isolated in this study were found to grow in the presence of 14 mM sodium arsenite (NaAsO2). In addition, the concentration of arsenic in five grams of Deparia lobatocrenata As-8 (EU476190) obtained from the Myoungbong abandoned mine area was 8,900 mg/kg ± 56.9, whereas the arsenic concentrations in the frond-rhizoplane of Pseudomonas putida GIST-MRP44-1 (EF623836), the root-rhizoplane of Acinetobacter sp. GIST-MRO62 (EF623849), and the stipe-rhizoplane of P. putida GIST-MRO63 (EF623850) were 41.9 mg/kg ± 1.0 (1 g of tissue), 32.9 mg/kg ± 0.9 (1 g of tissue), and 17.9 mg/kg ± 1.4 (1 g of tissue), respectively. Taken together, these findings suggest that the newly isolated indigenous fern-rhizobium, stipe-bacteria, and frond-bacteria may provide a better understanding of arsenic mobility in the field of molecular geomicrobiology and that it can be applied to the phytoremediation of arsenic-contaminated mines.  相似文献   

6.
Cytochrome b5 (b5) has been shown to modulate many cytochrome P450 (CYP)-dependent reactions. In order to elucidate the mechanism of such modulations, it is necessary to evaluate not only the effect of native b5 on CYP-catalyzed reactions, but also that of the apo-cytochrome b5 (apo-b5). Therefore, the apo-b5 protein was prepared using a heterologous expression in Escherichia coli. The gene for rabbit b5 was constructed from synthetic oligonucleotides using polymerase chain reaction (PCR), cloned into pUC19 plasmid and amplified in DH5α cells. The gene sequence was verified by DNA sequencing. The sequence coding b5 was cleaved from pUC19 by NdeI and XhoI restriction endonucleases and subcloned to the expression vector pET22b. This vector was used to transform E. coli BL-21 (DE3) Gold cells by heat shock. Expression of b5 was induced with isopropyl β-d-1-thiogalactopyranoside (IPTG). The b5 protein, produced predominantly in its apo-form, was purified from isolated membranes of E. coli cells by chromatography on a column of DEAE–Sepharose. Using such procedures, the homogenous preparation of apo-b5 protein was obtained. Oxidized and reduced forms of the apo-b5 reconstituted with heme exhibit the same absorbance spectra as native b5. The prepared recombinant apo-b5 reconstituted with heme can be reduced by NADPH:CYP reductase. The reconstituted apo-b5 is also fully biologically active, exhibiting the comparable stimulation effect on the CYP3A4 enzymatic activity towards oxidation of 1-phenylazo-2-hydroxynaphthalene (Sudan I) as native rabbit and human b5.  相似文献   

7.
8.
tRNAs are aminoacylated by the aminoacyl-tRNA synthetases. There are at least 20 natural amino acids, but due to the redundancy of the genetic code, 64 codons on the mRNA. Therefore, there exist tRNA isoacceptors that are aminoacylated with the same amino acid, but differ in their sequence and in the anticodon. tRNA identity elements, which are sequence or structure motifs, assure the amino acid specificity. The Seryl-tRNA synthetase is an enzyme that depends on rather few and simple identity elements in tRNASer. The Seryl-tRNA-synthetase interacts with the tRNASer acceptor stem, which makes this part of the tRNA a valuable structural element for investigating motifs of the protein–RNA complex. We solved the high resolution crystal structures of two tRNASer acceptor stem microhelices and investigated their interaction with the Seryl-tRNA-synthetase by superposition experiments. The results presented here show that the amino acid side chains Ser151 and Ser156 of the synthetase are interacting in a very similar way with the RNA backbone of the microhelix and that the involved water molecules have almost identical positions within the tRNA/synthetase interface.  相似文献   

9.
Methyl 4,6-O-benzylidene-2-deoxy-α--erythro-hexopyranosid-3-ulose reacted with potassium cyanide under equilibrating conditions to give, initially, methyl 4,6-O-benzylidene-3-C-cyano-2-deoxy-α--ribo-hexopyranoside (7), which, because it reverted slowly to the thermodynamically stable -arabino isomer, could be crystallised directly from the reaction mixture. The mesylate derived from the kinetic product 7 could be converted by published procedures into methyl 3-acetamido-2,3,6-trideoxy-3-C-methyl-α--arabino-hexopyranoside, which was transformed into methyl N-acetyl-α--vancosaminide on inversion of the configuration at C-4. A related approach employing methyl 2,6-dideoxy-4-O-methoxymethyl-α--erythro-hexopyranosid-3-ulose gave the kinetic cyanohydrin and thence, via the spiro-aziridine 27, methyl 3-acetamido-2,3,6-trideoxy-3-C-methyl-α--arabino-hexopyranoside, a known precursor of methyl N-acetyl-α--vancosaminide.  相似文献   

10.
The analysis by PC and/or GLC of the nectar sugars of about 30 species of Fritillaria confirms the well-known special position within the genus of F. imperialis, with no detectable sucrose, and underlines the distinction (proposed in a recent revision of the genus) between the species of the series Meleagris, with about equal fructose and glucose, and the members of the other series of section Trichostylae Boiss., which show a distinct preponderance of fructose over glucose.  相似文献   

11.

Background  

Because specific marker molecules for phenotypical identification of mesenchymal stem and progenitor cells are missing, the assessment of the in vitro-differentiation capacity is a prerequisite to characterize these cells. However, classical differentiation protocols are often cell-consuming and time intensive. Therefore, the establishment of novel strategies for differentiation is one topic of current efforts in stem cell biology. The goal of this study was to demonstrate the practicability of a new differentiation test using plastic adherent cell isolates from different tissues.  相似文献   

12.
The reaction of some dicarbonyl sugars with aminoguanidine.   总被引:1,自引:0,他引:1  
The reactions of aminoguanidine (guanylhydrazine) with 3-deoxy-D-erythro-hexos-2-ulose (1a), 3-deoxy-D-glycero-pentose-2-ulose (1b), D-erythro-hexos-2-ulose (1c), and D-glycero-pentose-2-ulose (1d) were examined at 37 degrees at a solution pH of 7.0 (phosphate buffer). For 1a and 1b, two major products were observed and shown respectively to be the 5- and 6-substituted 3-amino-1,2,4-triazine derivatives. The ratios of the products were independent of the amount of aminoguanidine present or the order of mixing the reagents prior to the experiments. For 1c and 1d, only the 5-substituted triazine derivatives were formed. No evidence for hydrazone or bishydrazone formation was observed.  相似文献   

13.
Specimens of Thecaphora saponariae s. lat. from several caryophyllacean host plants belonging to the genera Cerastium, Dianthus, Petrorhagia, Saponaria, Silene, and Stellaria were studied by means of both LM, SEM, and molecular phylogenetic analyses using ITS and LSU rDNA sequences. The data show that T. saponariae s. lat. is not uniform but represents several taxa. Molecular phylogenetic analyses, correlated with morphology of the sori, spore balls, and spores, permitted the recognition of five species. Two new species, Thecaphora italica and T. cerastii are described, and two new combinations, T. alsinearum and T. melandrii are proposed. The anamorph of Thecaphora saponariae is reported for the first time. A lectotype is designated for Sorosporium silenes-inflatae. Evolutionary aspects are discussed.  相似文献   

14.
Enzymatic synthesis of nucleotide sugars   总被引:5,自引:0,他引:5  
The present review gives a survey on the biosynthetic pathways of nucleotide sugars which are important for the in vitro synthesis of mammalian glycoconjugates. With respect to the use of these enzymes in glycotechnology the availability as recombinant enzymes from different sources, the large-scale synthesis of nucleotide sugars and their in situ regeneration in combination with glycosyltransferases are summarized and evaluated.  相似文献   

15.
Summary Nine pyrrolizidine alkaloids have been tested by the injection method for their ability to produce sex-linked recessive lethals in adult males ofDrosophila melanogaster. At a concentration of 0.02 M, monocrotaline, lasiocarpine and heliotrine were found to be strongly mutagenic. Echinatine, echimidine, senecionine and supinine were less active, while jacobine and platyphylline were only feebly mutagenic. In four cases tested, the N-oxides were found to be less active than their parent bases. The results are discussed in relation to the possibility that some of these alkaloids may be carcinogenic in man.With 1 Figure in the Text  相似文献   

16.
The reaction of 1,2:5,6-di-O-isopropylidene-3-C-methylene-α-D-ribo-hexofuranose (4) with mercuric azide in hot 50% aqueous tetrahydrofuran yielded, after reductive demercuration, 3-azido-3-deoxy-1,2:5,6-di-O-isopropylidene-3-C-methyl-α-D-glucofuranose (5). Partial, acid hydrolysis of5 afforded the diol7, which gave 3-azido-3-deoxy-1,2-O-isopropylidene-5,6-di-O-methanesulphonyl-3-C-methyl-α-D-glucofuranose (8) on sulphonylation. On hydrogenation over a platinum catalyst and N-acetylation, the dimethanesulphonate 8 furnished 3,6-acetylepimino-3,6-dideoxy-1,2-O-isopropylidene-5-O-methanesulphonyl-3-C-methyl-α-D-glucofuranose (9), which was also prepared by an analogous sequence of reactions on 3-azido-3-deoxy-1,2-O-isopropylidene-5-O-methanesulphonyl-3-C-methyl-6-O-toluene-p-sulphonyl-α-D-glucofuranose (13). The formation of the N-acetylepimine 9 establishes the D-gluco configuration for 5.1,2-O-Isopropylidene-3-C-methylene-α-D-ribo-hexofuranose (20) reacted with mercuric azide in aqueous tetrahydrofuran at ≈85° to give 3,6-anhydro-1,2-O-isopropylidene-3-C-methyl-α-D-glucofuranose (22) as a result of intramolecular participation by the C-6 hydroxyl group in the initial intermediate.  相似文献   

17.
18.
Treatment of tetra-O-acetyl-β-d-glucopyranosyl N,N-dimethyldithiocarbamate (1) with phenylmercury(II) acetate gives tetra-O-acetyl-1-phenylmercury(II)thio-β-d-glucopyranose (3), which can also be made in high yield from other dithiocarbamates, from tetra-O-acetyl-1-thio-β-d-glucopyranose, and from its S-acetyl derivative. The p-diethylamino derivative (7) of compound 3 displays significantly different properties and is readily convertible into bis(tetra-O-acetyl-1-thio-β-d-glucopyranosyl)mercury(II) (8), which is also obtainable by treatment of tetra-O-acetyl-1-thio-β-d-glucopyranose with mercury(II) acetate. Aspects of the chemistry of compounds 3, 7, and 8 are reported; demercuration of 3 affords a convenient synthesis of 2,3,4,6-tetra-O-acetyl-1-thio-β-d-glucose.  相似文献   

19.
Summary By labelling wild-type Bacillus subtilis for 5 min with [35S]-methionine either at the time of resuspension in starvation medium or 1, 2 or 3 h later, and subjecting cell extracts to two-dimensional gel electrophoresis, Yudkin et al. (J. Gen. Microbiol. 1982) detected some 75 proteins whose synthesis started or stopped within the first 3 h of sporulation. Similar experiments have now been done with isogenic strains carrying a spoOA or a spoIIA mutation. The results permit 72 of the changes in protein synthesis to be placed in four classes according to whether they do or do not occur in the mutants as well as in the wild type. The results are in good agreement with the predictions of the dependent-sequence hypothesis, which states that each event that occurs in sporulation depends on the successful completion of all preceding events. The pattern of protein synthesis in the spoIIA mutant differed in some respects from the wild type as early as 1 h after resuspension.  相似文献   

20.
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