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41.
42.
Michael L. Mavrovouniotis Patrick Bayol Tu-Kien Michael Lam George Stephanopoulos Gregory Stephanopoulos 《Biotechnology Techniques》1988,2(1):23-28
Using Gibbs Energies of compounds, as well as Gibbs Energy changes and equilibrium constants of biochemical reactions, the contributions of functional groups to the Gibbs Energy (in aqueous solution, temperature 25°C, and pH=7) have been estimated. These contributions allow the estimation of the Gibbs Free Energy and the equilibrium constant of a biochemical reaction, given the structure of the reactants and products. 相似文献
43.
44.
Alterations in lipid content and composition in the N-nitrosodiethylamine-induced hepatocarcinoma were investigated. Rats were administrated with N-nitrosodiethylamine in the drinking water for 12 weeks followed by normal tap water for another 6 weeks. The cholesterol content in the liver was increased shortly after the administration of N-nitrosodiethylamine and remained elevated after the removal of the nitrosoamine from the water. The phosphatidylethanolamine level was elevated during N-nitrosodiethylamine administration with a concomitant reduction in phosphatidylcholine level. Lysophosphatidylcholine and sphingomyelin levels were increased during the last four weeks of the study. The level of phosphatidylinositol was substantially reduced after eight weeks of N-nitrosodiethylamine treatment, and remained low during the post-treatment period. We postulate that changes in lysophosphatidylcholine and sphingomyelin may be a compensatory mechanism for maintaining the asymmetrical distribution of choline-containing lipids in the outer leaflet of the membrane. The elevated level of cholesterol may be a useful indicator for the early detection of N-nitrosodiethylamine-induced hepatocarcinoma. 相似文献
45.
Synopsis We investigated the ability of two congeneric species of sunfish to learn to forage on a novel prey item in feeding arenas
containing structured habitats. Eight bluegill sunfish and eight pumpkinseed sunfish were given the opportunity to forage
on whiteworms daily for 10 days. Each day, several behavioural measures were recorded for each fish. Both species of sunfish
learned to feed over the 10-day period but the bluegill sunfish learned to feed more quickly than the pumpkinseed sunfish.
Pumpkinseeds, however, attained a higher level of foraging efficiency. The differences in learning and foraging efficiency
were related to body morphology. 相似文献
46.
47.
The organotypic culture of human skin keratinocytes and fibroblasts to achieve form and function 总被引:6,自引:0,他引:6
Dr. Nancy L. Parenteau Patrick Bilbo Cynthia J. M. Nolte Valerie S. Mason Mireille Rosenberg 《Cytotechnology》1992,9(1-3):163-171
We describe an organotypic model of human skin comprised of a stratified layer of human epidermal keratinocytes and dermal
fibroblasts within a contracted collagen lattice. Feasible and reproducible production of the skin construct has required
the use of traditional as well as specialized culture techniques. The configuration of the construct has been engineered to
maintain polarity and permit extended culture at the air-liquid interface. Morphological, biochemical and kinetic parameters
were assessed and functional assays were performed to determine the degree of similarity to human skin. Light and ultrastructural
morphology of the epidermis closely resembled human skin. The immunocytochemical localization of a number of differentiation
markers and extracellular matrix proteins was also similar to human skin. Kinetic data showed a transition of the epidermal
layer to a morein vivo-like growth rate during the development of the construct at the air-liquid interface. The barrier properties of the construct
also increased with time reaching a permeability to water of less than 2%·h after approximately 2 weeks at the air-liquid
interface which is still on average 30-fold more water-permeable than normal human skin. The construct is currently used forin vitro research and testing and is also being tested in clinical applications. 相似文献
48.
Summary Auxin (indole-3-acetic acid) is considered to be an important signalling molecule in the regulation of plant growth and development but neither auxin synthesis nor its mode of action is clearly understood. To identify genes involved in these processes, mutations were sought that altered the auxin requirement of plant tissues for growth. For the first time mutant plants were obtained that carry a recessive mutation at a single nuclear locus (auxl) which results in an absolute requirement for exogenous auxin for normal growth. In the absence of auxin treatment, mutant plants undergo premature senescence and die.Abbreviations BAP
6-benzylaminopurine
- BUdR
5-bromodeoxyuridine
- 2,4-D
2,4-dichlorophenoxyacetic acid
- FUdR
5-fluorodeoxyuridine
- IAA-EE
indole-3-acetic acid ethyl ester
- IMS
indole-3-methanesulfonic acid 相似文献
49.
Aluminium,boron and molybdenum availability and uptake by rice in acid sulfate soils 总被引:1,自引:0,他引:1
Although Al toxicity is believed to be a problem in acid sulfate soils cropped to rice (Oryza, sativa L.), little is known about the behavior of other trace metals such as B and Mo in these soils. The objectives of this study were to measure the availability of Al, B, and Mo in these soils, to determine what governs the availability of these metals and to investigate the relationships between metal availability and uptake by rice. Metal availability and uptake by rice were evaluated in 134 flooded acid sulfate soils in the Central Plains region of Thailand and in a growth chamber study using 50 of the same soils. Soil and plant metal analyses were conducted at the panicle differentiation stage of growth in both studies and in the soil prior to transplanting in the growth chamber study. Metal activities were determined with GEOCHEM. The mineral phases believed to be governing Al3+ activities were jurbanite under low pH conditions and amorphous Al(OH)3 at high pH. The Al chemistry is believed to be intimately linked to the redox-pH cycle, which is driven by the monsoonal climate. Mortality of rice associated with Al toxicity was observed under field and growth chamber conditions. Interference in P uptake and/or assimilation was believed to be the mechanism of Al toxicity. Activities of B(OH)
4
–
and B(OH)
3
0
were found to be highly correlated to pH and ionic strength, respectively, with the latter being the dominant B ion found in these soils. Activities of MoO
4
2–
were positively correlated to pH and appeared to be controlled by wulfenite. Leaf Mo contents were found to be positively correlated with MoO
4
2–
activity. 相似文献
50.
The permeability of bacterial outer membranes was assayed by coupling the influx of highly hydrophobic probes, 3-oxosteroids, with their subsequent oxidation catalysed by 3-oxosteroid delta 1-dehydrogenase, expressed from a gene cloned from Pseudomonas testosteroni. In Salmonella typhimurium producing wild-type lipopolysaccharide, the permeability coefficients for uncharged steroids were 0.45 to 1 x 10(-5) cm s-1, and the diffusion appeared to occur mainly through the lipid bilayer domains of the outer membrane. These rates are one or two magnitudes lower than that expected for their diffusion through the usual biological membranes. The permeation rates were markedly increased (up to 100 times) when the lipopolysaccharide leaflet was perturbed either by adding deacylpolymyxin or by introducing mutations leading to the production of deep rough lipopolysaccharides. An amphiphilic, negatively charged probe, testosterone hemisuccinate, penetrated much more slowly than the uncharged steroids. Study of various Gram-negative species revealed that P. testosteroni, Pseudomonas acidovorans, and Acinetobacter calcoaceticus showed higher outer membrane permeability to steroid probes and higher susceptibility to hydrophobic agents such as fusidic acid, novobiocin and crystal violet relative to S. typhimurium and Escherichia coli. 相似文献