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1.
2.
The reactions of aliphatic and aromatic amines with reducing sugars are important in both drug stability and synthesis. The
formation of glycosylamines in solution, the first step in the Maillard reaction, does not typically cause browning but results
in decreased potency and is hence significant from the aspect of drug instability. The purpose of this research was to present
(1) unreported ionic equilibria of model reactant (kynurenine), (2) the analytical methods used to characterize and measure
reaction products, (3) the kinetic scheme used to measure reaction rates and (4) relevant properties of various reducing sugars
that impact the reaction rate in solution. The methods used to identify the reversible formation of two products from the
reaction of kynurenine and monosaccharides included LC mass spectrometry, UV spectroscopy, and 1-D and 2-D 1H–1H COSY NMR spectroscopy. Kinetics was studied using a stability-indicating HPLC method. The results indicated the formation
of α and β glycosylamines by a pseudo first-order reversible reaction scheme in the pH range of 1–6. The forward reaction
was a function of initial glucose concentration but not the reverse reaction. It was concluded that the reaction kinetics
and equilibrium concentrations of the glycosylamines were pH-dependent and also a function of the acyclic content of the reacting
glucose isomer. 相似文献
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CONRAD J. HOSKIN HAMISH McCALLUM † 《Biological journal of the Linnean Society. Linnean Society of London》2007,92(3):593-603
Parasites could differentially impact intraspecific host lineages due to genetic, phenotypic, ecological, or behavioural differences between the lineages, or the development of reproductive isolation between them. Batrachomyia (Diptera: Chloropidae) are flies that exclusively parasitize Australian frogs, and in the Wet Tropics rainforest of north‐east Australia larvae are largely restricted to the green‐eyed tree frog Litoria genimaculata (Anura: Hylidae). This frog species consists of two highly divergent genetic lineages that overlap in two nearby, but independent, contact zones. At one contact zone there has been extensive phenotypic divergence and speciation between the lineages whereas, at the other contact relatively lower levels of phenotypic divergence and reproductive isolation suggest that speciation has not occurred. In the present study we tested: (1) whether the deep phylogeographic divergence between northern and southern host populations is mirrored by congruent genetic structuring in the parasite populations and (2) whether the host lineages are differentially impacted by parasitism. We found that the two divergent frog lineages are parasitized by a single lineage of Batrachomyia, which exhibits strikingly little phylogeographic structuring. We found a significant difference in Batrachomyia prevalence between the host lineages at mixed lineage sites in both contact zones, with the magnitude and direction of this effect being consistent in both. The pattern did not differ between the two contacts even though recent phenotypic divergence and speciation has occurred between the lineages at one contact but not the other. Taken together, this suggests a fundamental difference in susceptibility between the genetically divergent host lineages. Using weight relative to body length as a measure of body condition, we found no differential impact of parasitism on the body condition of each host lineage, and no evidence that parasitism impacts the body condition of the host in general. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92 , 593–603. 相似文献
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The influence of CO2 enrichment, phosphorus deficiency and water stress on the growth, conductance and water use of Pinus radiata D. Don 总被引:10,自引:4,他引:6
JANN P. CONROY M. KÜPPERS B. KÜPPERS J. VIRGONA E. W. R. BARLOW 《Plant, cell & environment》1988,11(2):91-98
Abstract. Seedlings of Pinus radiata D. Don were grown in growth chambers for 22 weeks with two levels of phosphorus, under either well-watered or water-stressed conditions at CO2 concentrations of either 330 or 660mm3 dm?3. Plant growth, water use efficiency and conductance were measured and the relationship between these and needle photosynthetic capacity, water use efficiency and conductance was determined by gas exchange at week 22. Phosphorus deficiency decreased growth and foliar surface area at both CO2concentrations; however, it only reduced the maximum photosynthetic rates of the needles at 660 mm3 CO2 dm?3 (plants grown and measured at the same CO2 concentration). Water stress reduced growth and foliar surface area at both CO2 concentrations. Increases in needle photosynthetic rates appeared to be partly responsible for the increased growth at high CO2 where phosphorus was adequate. This effect was amplified by accompanying increases in needle production. Phosphorus deficiency inhibited these responses because it severely impaired needle photosynthetic function. The relative increase in growth in response to high CO2 was higher in the periodically water-stressed plants. This was not due to the maintenance of cell volume during drought. Plant water use efficiency was increased by CO2 enrichment due to an increase in dry weight rather than a decrease in shoot conductance and, therefore, transpirational water loss. Changes in needle conductance and water use efficiency in response to high CO2 were generally in the same direction as those at the whole plant level. If the atmospheric CO2 level reaches the predicted concentration of 660 mm3 dm?3 by the end of next Century, then the growth of P. radiata will only be increased in areas where phosphorus nutrition is adequate. Growth will be increased in drought-affected regions but total water use is unlikely to be reduced. 相似文献
7.
Physiological effects of five months exposure to low concentrations of O3 and NH3 on Douglas fir (Pseudotsuga menziesii) 总被引:2,自引:0,他引:2
Three years old seedlings of Douglas fir (Pseudotsuga menziesii) were exposed lo filtered air, O3 (day and night concentrations of 78 and 30 μgm?3: respectively). NH3 (54 μg m?3) and to a mixture of NH3+O3 (day and night concentrations of 49 + 83 and 49 + 44 μg m?3 respectively), for 5 months in fumigation chambers. Both gas exchange and chlorophyll fluorescence were measured on shoots which had sprouted at the beginning of the exposure period. After 4. 8, 10 and 20 weeks of exposure, light response curves of electron transport rate (J) were determined, in which J was deduced from chlorophyll fluorescence. Net CO2 assimiialion was measured at maximum light intensity of 560) μmol m?2 S?1 (Pn.560). After 8 and 10 weeks of exposure also light response curves of CO2 assimilation were assessed. Shoots exposed to O3 showed a reduction in net CO2 assimilation as compared to the control shoots during the entire exposure period. The reduction was related lo a lower chlorophyll content and a lower electron transport rate, whereas no effect on quantum yield efficiency (qy) was observed. In contrast, shoots exposed to NH3 showed a positive effect on photosynthesis. Shoots exposed to NH3. + O3 showed a rapid increase in Pn.560, in the period between 4 and 8 weeks to a level equal of that of the NH3-treatment. After this period a decline in Pn.560 was observed. After 10 weeks of exposure shoots exposed to O3 showed an increased transpiration rate in the dark as compared to the control shoots. In addition, water use efficiency (WUE) declined as a result of an increase in leaf conductance. Both observations indicate that the stomatal apparatus was affected by O3. A high transpiration rate in the dark was also found for shoots esposed to NHX. However, shoots exposed to NH3+ O3 showed neither an effect on WUE, nor an effect on transpiration rate in the dark. The possibility that NH3 delayed the O3 induced effects on photosynthesis and stomatal conductance is discussed. 相似文献
8.
CO dehydrogenase/acetyl-CoA synthase (CODH/ACS) is one of the four known nickel enzymes. It is a bifunctional protein that
catalyzes the oxidation of CO to CO2 at a nickel iron-sulfur cluster (Cluster C) and a remarkable condensation reaction between a methyl group (donated from a
methylated corrinoid iron-sulfur protein), carbon monoxide, and coenzyme A to form acetyl-CoA at a separate nickel iron-sulfur
cluster (Cluster A). This review focuses on the current understanding of the structure and function of Cluster A and on related
model chemistry. It describes studies that uncovered the first example of a biological organometallic reaction sequence. The
mechanism of acetyl-CoA synthesis includes enzymebound methylnickel, iron-carbonyl, and acylmetal intermediates. Discovery
of the methylnickel species constituted the first example of an alkylnickel species in biology and unveiled a new biological
role for nickel.
Received: 10 April 1996 / Accepted: 4 July 1996 相似文献
9.
Effect of hydrogen sulfide on growth of sulfate reducing bacteria 总被引:20,自引:0,他引:20
A culture of sulfate reducing bacteria (SRB) growing on lactate and sulfate was incubated at different pH values in the range of 5.8-7.0. The effect of pH on growth rate was determined in this pH range; the highest growth rate was observed at pH 6.7. Hydrogen sulfide produced from sulfate reduction was found to have a direct and reversible toxicity effect on the SRB. A hydrogen sulfide Concentration of 547 mg/L (16.1 mM) completely inhibited the culture growth. Comparison between acetic acid and hydrogen sulfide inhibition is presented and the concomitant inhibition kinetics are mathematically described. (c) 1992 John Wiley & Sons, Inc. 相似文献
10.
Two rice ( Oryza sativa L.) cultivars of contrasting morphologies, IR-36 and Fujiyama-5, were exposed to ambient (360 μl l−1 ) and ambient plus 300 μl l−1 CO2 from time of emergence until ca 50% grain fill at the Duke University Phytotron, Durham, North Carolina. Exposure to increased CO2 resulted in about a 50% increase in the photosynthetic rate for both cultivars and photosynthetic enhancement was still evident after 3 months of exposure to a high CO2 environment. The photosynthetic response at 5% CO2 and the response of CO2 assimilation (A) to internal CO2 (Ci ) suggest a reallocation of biochemical resources from RuBP carboxylation to RuBP regeneration. Increases in total plant biomass at elevated CO2 were approximately the same in both cultivars, although differences in allocation patterns were noted in root/shoot ratio. Differences in reproductive characteristics were also observed between cultivars at an elevated CO2 environment with a significant increase in harvest index for IR-36 but not for Fujiyama-5. Changes in carbon allocation in reproduction between these two cultivars suggest that lines of rice could be identified that would maximize reproductive output in a future high CO2 environment. 相似文献