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《Biorheology》1995,32(2-3):143-144
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Philip A.J. Gorin 《Carbohydrate research》1982,101(1):13-20
The four isomers of methyl O-β-d-galactopyranosyl-β-d-galactopyranoside were prepared by condensation of 2,3,4,6-tetra-O-acetyl-α-d-galactopyranosyl bromide with appropriate, partially O-substituted derivatives of methyl β-d-galactopyranoside. Reaction of 3,4,6-tri-O-acetyl-1,2-O-(1-ethoxyethylidene)-α-d-galactopyranose with the same acceptors, in the presence of mercuric bromide, led to the formation of α and β linkages. Thus, it was possible to assign 13C-n.m.r. resonances of α and β anomers of methyl O-d-galactopyranosyl-β-d-galactopyranosides. In terms of application of these shift values and those of related d-galactobioses to the structural analysis of d-galactopyranans by shift comparisons, some generalizations can be made. For β-d-galactopyranans, the resonances of glycosyloxylated carbon atoms of methyl O-β-d-galactopyranosyl-β-d-galactopyranosides are sensitive to structure and appear to have typical values, whereas limited variation was observed with shifts of C-1′ signals. On the other hand, for assigning structures to d-galactopyranans containing α linkages, the C-1′ shifts (at higher field) of methyl O-α-d-galactopyranosyl-β-d-galactopyranosides are sensitive to linkage position, whereas those of glycosyloxylated carbon atoms vary only a little. 相似文献
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From pollen grains of Typha davidiana, T. latifolia, T. angustata the same eight
flavonoids have been isolated. They are identified as naringenin I, isorhamnetin II, quercetin
III, isorhamnetin-3-O-(2G-α-L-rhamnopyranosyl)-rutioside IV, quercetin-3-O-(2G-α-L-rhamnopyranosyl)-rutinosida, V, isorhamnetio-3-O-rutinoside VI, isorhamnetino-3-O-neohesperidoside VII,
kampferol-3-O-neohesperidoside VIII. Flavonoids of pollen grains of five species of Typha, including the above three species, were analysed by TLC with the result showing that the constituents in the pollen grains of the five species are very similar.
The chemical comparison among Typha and Sparganium and 16 possibly related families
shows that Typha is different from Pandanaceae or Pandanales and is similar to Restionaceae,
Flagellariaceae, Juncaceae and Cyperaceae in some respects. Typha and Sparganium are very
similar in many respects, and they could be treated in the same family, Typhaceae, which merit
the rank of order, Typhales. 相似文献
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J. P. Fonseca A. Levy R. Henriques J. C. Costa C. Neto J. Robalo 《Plant biosystems》2016,150(4):787-798
In this paper, we analyzed the phylogeny of the section Bulbocodii (genus Narcissus; Amarillydaceae) using the matK and trnL-F fragments of cpDNA in order to review the validity of the recognized taxa. Our results indicate that Narcissus obesus should be considered a valid species, and that N. blancoi is a distinct taxon. In addition, seven previously recognized species, N. juressianus, N. subnivalis, N. graellsii, N. conspicuus, N. citrinus, N. nivalis, and N. quintanilhae, should be assigned to an infraspecific rank under N. bulbocodium, as they are not valid species. In addition, we analyzed the distribution of the three morphological characters widely used in the systematics of this section and found that their variation does not agree with the phylogenetic results, rendering these characters limited taxonomical utility. This result suggests that the section Bulbocodii shows high morphological lability, which can explain the proliferation of nominal species. 相似文献
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Microbial metabolism of aromatic nitriles. Enzymology of C–N cleavage by Nocardia sp. (Rhodochrous group) N.C.I.B. 11216
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David B. Harper 《The Biochemical journal》1977,165(2):309-319
1. An organism utilizing benzonitrile as sole carbon and nitrogen source was isolated by the enrichment-culture technique and identified as a Nocardia sp. of the rhodochrous group. 2. Respiration studies indicate that nitrile degradation proceeds through benzoic acid and catechol. 3. Cell-free extracts of benzonitrile-grown cells contain an enzyme that catalyses the conversion of benzonitrile directly into benzoic acid without intermediate formation of benzamide. 4. This nitrilase enzyme was purified by DEAE-cellulose chromatography and gel filtration on Sephadex G-100 in the presence and absence of substrate. The purity of the enzyme was confirmed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and isoelectric focusing on polyacrylamide gel. 5. The enzyme shows a time-dependent substrate-activation process in which the substrate catalyses the association of inactive subunits of mol.wt. 45000 to form the polymeric 12-unit active enzyme of mol.wt. 560000. The time required for complete association is highly dependent on the concentration of the enzyme, temperature and pH. 6. The associated enzyme has a pH optimum of 8.0 and K(m) with benzonitrile as substrate of 4mm. The activation energy of the reaction as deduced from the Arrhenius plot is 51.8kJ/mol. 7. Enzyme activity is inhibited by thiol-specific reagents and several metal ions. 8. Studies with different substrates indicate that the nitrilase is specific for nitrile groups directly attached to the benzene ring. Various substituents in the ring are compatible with activity, though ortho-substitution, except by fluorine, renders the nitrile invulnerable to attack. 9. The environmental implications of these findings and the possible significance of the enzyme in the regulation of metabolism are discussed. 相似文献
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I. Y. Rauschenbach L. B. Golosheikina L. S. Korochkina L. I. Korochkin 《Biochemical genetics》1977,15(5-6):531-548
From analysis of the properties of the pupal esterase (p-esterase) in Drosophila virilis, it is concluded that it is heat stable, its electrophoretic detection depends on culture density, its expression is stage specific, and it is not a variant of esterase 2. It was also demonstrated that p-esterase, like esterase 6, is activated by injections of the juvenile hormone into larvae. Heat treatment of heat-resistant D. virilis stocks led to decreased activities of the juvenile hormone dependent esterases but did not affect those of the heat-sensitive stocks. It is suggested that heat resistance in D. virilis is related to some functional features of the system of modifier genes controlling the phenotypic expression of esterases. 相似文献
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Marchal LM Ulijn RV De Gooijer CD Franke GT Tramper J 《Bioprocess and biosystems engineering》2003,26(2):123-132
A model is presented that describes all the saccharides that are produced during the hydrolysis of starch by an -amylase. Potato amylopectin, the substrate of the hydrolysis reaction, was modeled in a computer matrix. The four different subsite maps presented in literature for -amylase originating from Bacillus amyloliquefaciens were used to describe the hydrolysis reaction in a Monte Carlo simulation. The saccharide composition predicted by the model was evaluated with experimental values. Overall, the model predictions were acceptable, but no single subsite map gave the best predictions for all saccharides produced. The influence of an (16) linkage on the rate of hydrolysis of nearby (14) linkages by the -amylase was evaluated using various inhibition constants. For all the subsites considered the use of inhibition constants led to an improvement in the predictions (a decrease of residual sum of squares), indicating the validity of inhibition constants as such. As without inhibition constants, no single subsite map gave the best fit for all saccharides. The possibility of generating a hypothetical subsite map by fitting was therefore investigated. With a genetic algorithm it was possible to construct hypothetical subsite maps (with inhibition constants) that gave further improvements in the average prediction for all saccharides. The advantage of this type of modeling over a regular fit is the additional information about all the saccharides produced during hydrolysis, including the ones that are difficult to measure experimentally. 相似文献
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Summary The effects of N-methyl-N–nitro-N-nitroso-guanidine (NTG) on protoplasts of Streptomycetes are markedly different from its action on spores, showing high mutagenic activity even at concentrations having no marked effect on protoplast survival. Strain improvement, eg in chlorotetracycline-producing strains of S. aureofaciens, was most effective when protoplasts were subjected to prolonged treatment (2 h) with low concentrations of NTG (50 /ug/ml). 相似文献
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