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91.
Søren Bak Rachel Alice Kahn Carl Erik Olsen Barbara Ann Halkier 《The Plant journal : for cell and molecular biology》1997,11(2):191-201
Obtusifoliol 14β-demethylase from Sorghum bicolor (L.) Moench has been cloned using a gene-specific probe generated using PCR primers designed from an internal 14 amino acid sequence. The sequence identifies sorghum obtusifoliol 14α-demethylase as a cytochrome P450 and it is assigned to the CYP51 family together with the sterol 14α-demethylases from fungi and mammals. The presence of highly conserved regions in the amino acid sequences, analogous substrates and the same metabolic role demonstrate that the sterol 14α-demethylases are orthologous enzymes. The sterol 14α-demethylases catalyse an essential step in sterol biosynthesis as evidenced by the absence of a 14α-methyl group in all known functional sterols. A functional sorghum obtusifoliol 14α-demethylase was expressed at high levels in Escherichia coli and purified using an efficient method based on temperature-induced Triton X-114 phase partitioning. The recombinant purified enzyme produced a type I spectrum with obtusifoliol as substrate. Reconstitution of purified recombinant enzyme with sorghum NADPH—cytochrome P450 reductase in dilaurylphosphatidylcholine micelles confirms that obtusifoliol 14α-demethylase catalyses the 14α-demethylation of obtusifoliol to 4α-methyl-5α-ergosta-8,14,24(28)-trien-3β-ol as evidenced by GC—MS. The isolation of a cDNA clone encoding the plant sterol 14α-demethylase, combined with the previously isolated cDNA clones for fungal and mammalian sterol 14α-demethylases, provides an important tool in the rational design of specific inhibitors towards the individual sterol 14α-demethylases. 相似文献
92.
Charlotte Schou Erik R. Ottosen Hans Jørgen Petersen Fredrik Björkling Scilla Latini Pernille V. Hjarnaa Erik Bramm Lise Binderup 《Bioorganic & medicinal chemistry letters》1997,7(24):616-3100
4-Pyridyl cyanoguanidines with hydrophobic aromatic side chains showed potent antiproliferative activity in the human breast and lung cancer cell lines MCF-7, NYH and H460. In vivo, treatment with N-(6-chlorophenoxyhexyl)-N′-cyano-N″-4-pyridylguanidine (18, 20 mg/kg/day po.), gave a complete remission of tumours in a model of NYH inoculated nude mice. 相似文献
93.
Vertical displacement velocity of a Daphniagaleata × hyalina clone was quantified inrelation to changes in the relative rate of lightchange. An increase in the latter variable triggers anenhanced swimming response, and this response is againelicited when a second increase in the rate ofrelative light increase is applied. Decreases in therate of light increase affect phototactic swimming ina similar way. The acceleration/deceleration assistedstimulus-response system is an extension of the ideaof phototaxis as the underlying behavioural mechanismfor vertical migration, and suggests that continuousaccelerations in light change also affect verticaldisplacements observed in the field. A simple dielvertical migration simulation model was used tocalculate the vertical displacement of Daphniain relation to the natural light change at sunrise.The calculated vertical displacement fits nicely inthe temporal range of the observed averaged downwardmigration of adult Daphnia in Lake Maarsseveen.The calculated migration amplitude, however, islarger than the change in mean population depthobserved in nature. 相似文献
94.
Surface water chemistry characteristics in the Lake Storgrønningen drainage area, Høylandet, during periods of high and low discharge 总被引:2,自引:2,他引:0
The surface water chemistry of Høylandet has beenstudied by performing two synoptic surveys, duringhigh runoff in the autumn of 1986 and during a lowflow period in the summer of 1988. Based on watersamples of up to 38 chemical variables from 75 sites,analyses show considerable variation in the chemicalcomposition. There is a strong altitude gradient, i.e.very dilute poorly buffered waters dominate at higherelevations near the timberline while progressivelyhigher salt content and alkalinities arecharacteristic at lower altitudes more dominated byforests. The influence of mires is less pronounced.The overall water quality is of oligotrophic naturewith low concentrations of strong acid anions andmetals known to be enriched under acidifiedconditions. The natural pH gradients are considerablebut with no indication of anthropogenic acidification.The data provide little support for the hypothesisthat in-catchment production of organically derivedacidity leads to acid runoff, which in thesecatchments appears compensated by increasedweathering. The findings are in general accordancewith other Høylandet catchment studies. It isconcluded that this area may serve as a representativepristine surface runoff analogue for catchmentscurrently affected by atmospheric deposition of strongmineral acids. 相似文献
95.
Removal of toluene in waste gases using a biological trickling filter 总被引:12,自引:0,他引:12
The removal of toluene from waste gas was studied in a trickling biofilter. A high level of water recirculation (4.7 m h–1) was maintained in order to keep the liquid phase concentration constant and to achieve a high degree of wetting. For loads in the range from 6 to 150 g m–3 h–1 the maximum volumetric removal rate (elimination capacity) was 35±10 g m–3 h–1, corresponding to a zero order removal rate of 0.11±0.03 g m–2 h–1 per unit of nominal surface area. The surface removal was zero order above the liquid phase concentrations of approximately 1.0 g m–3, corresponding to inlet gas concentrations above 0.7–0.8 g m–3. Below this concentration the surface removal was roughly of first order. The magnitude of the first order surface removal rate constant, k1A
, was estimated to be 0.08–0.27 m h–1 (k1A
a=24–86 h–1). Near-equilibrium conditions existed in the gas effluent, so mass transfer from gas to liquid was obviously relatively fast compared to the biological degradation. An analytical model based on a constant liquid phase concentration through the trickling filter column predicts the effluent gas concentration and the liquid phase concentration for a first and a zero order surface removal. The experimental results were in reasonable agreement with a very simple model valid for conditions with an overall removal governed by the biological degradation and independent of the gas/liquid mass transfer. The overall liquid mass transfer coefficient, KLa, was found to be a factor 6 higher in the system with biofilm compared to the system without. The difference may be explained by: 1. Difference in the wetting of the packing material, 2. Mass transfer occurring directly from the gas phase to the biofilm, and 3. Enlarged contact area between the gas phase and the biofilm due to a rough biofilm surface. 相似文献
96.
Modeling the leech heartbeat elemental oscillator I. Interactions of intrinsic and synaptic currents
Farzan Nadim Øystein H. Olsen Erik de Schutter Ronald L. Calabrese 《Journal of computational neuroscience》1995,2(3):215-235
We have developed a biophysical model of a pair of reciprocally inhibitory interneurons comprising an elemental heartbeat oscillator of the leech. We incorporate various intrinsic and synaptic ionic currents based on voltage-clamp data. Synaptic transmission between the interneurons consists of both a graded and a spike-mediated component. By using maximal conductances as parameters, we have constructed a canonical model whose activity appears close to the real neurons. Oscillations in the model arise from interactions between synaptic and intrinsic currents. The inhibitory synaptic currents hyperpolarize the cell, resulting in activation of a hyperpolarization-activated inward currentI
h
and the removal of inactivation from regenerative inward currents. These inward currents depolarize the cell to produce spiking and inhibit the opposite cell. Spike-mediated IPSPs in the inhibited neuron cause inactivation of low-threshold Ca++ currents that are responsible for generating the graded synaptic inhibition in the opposite cell. Thus, although the model cells can potentially generate large graded IPSPs, synaptic inhibition during canonical oscillations is dominated by the spike-mediated component. 相似文献
97.
Defective regulation of the cytosolic Ca2+ activity in parathyroid cells from patients with hyperparathyroidism 总被引:2,自引:0,他引:2
Rolf Larsson Chris Wallfelt Håkan Abrahamsson Erik Gylfe Sverker Ljunghall Jonas Rastad Patrik Rorsman Leif Wide Göran Åkerström 《Bioscience reports》1984,4(11):909-915
The parathyroid hormone (PTH) release and cytosolic Ca2+ activity were determined in normal bovine parathyroid cells and parathyroid cells obtained from patients with hyperparathyroidism (HPT). There was a sigmoid relation between the cytosolic Ca2+ activity and the extracellular calcium concentration between 0.5 and 6.0 mmol/l. The PTH release was inhibited in parallel with the rise in the cytosolic Ca2+ activity. Both the hormone release and the cytosolic Ca2+ activity were lower in cells from human adenomas and hyperplastic glands~ and in comparison with the bovine preparations these ceils had higher set points for the cytosolic Ca2+ activity and PTH release. There was a close correlation between the individual set points for the cytosolic Ca2+ activity and PTH release in a material containing both normal and pathological cells. The results indicate that the abnormal PTH release characteristic of HPT is due to a defective regulation of the cytosolic Ca2+ activity. 相似文献
98.
Sven Erik Godtfredsen Anne Munk Rasmussen Martin Ottesen Peer Rafn Nicolai Peitersen 《Applied microbiology and biotechnology》1984,20(1):23-28
Summary Acetolactate decarboxylase activity has been detected among three genera, nine species and 263 strains of lactic acid bacteria tested in the course of a screening for acetolactate decarboxylases amenable for use in brewing as maturation aid. Streptococcus diacetylactis strain FD-64-D was found to generate a decarboxylase exhibiting a satisfactory activity and an excellent stability at the pH prevailing in beer and wort. This decarboxylase could not be solubilized but enzymatically active, freeze-dried cells were effective for satisfactory flavour maturation of beer although difficulties were encountered during attempts to remove the applied cell material by filtration of the beer. Lactobacillus casei DSM 2547 was likewise found to produce a decarboxylase exhibiting a satisfactory activity and stability at the low pH of beer and which, in addition, was readily solubilized. A method has been developed for pilot scale production of preparations of this decarboxylase suitable for use in brewing.Abbreviations DSM
Deutsche Sammlung von Microorganismen
- EDTA
Ethylene diaminetetra-acetic acid 相似文献
99.
The natural mortality rate of trout fry and the impact of weed cutting and cleaning out of weeds, branches and twigs from the stream-bed upon the mortality rate of trout fry was studied on several reaches in small streams. Above an initial density of 3.1 fry m–2 natural mortality rate was found to be density-dependent in the first few months of life. In reaches where weed cutting and cleaning out of the stream-bed had taken place the mortality rate was higher than that found under natural conditions in undisturbed reaches. The results support the suggestion that stream management works which make the stream more uniform will be in conflict with sound fishery management. 相似文献
100.
Rino Cella Roberta Colombo Maria Grazia Galli Erik Nielsen Franco Rollo Francesco Sala 《Physiologia plantarum》1982,55(3):279-284
Rice ( Oryza sativa L.) cells returning to in vitro culture after preservation at superlow temperature in liquid nitrogen are characterized by a number of physiological alterations. These include: reduction in respiration and glucose uptake, loss of intracellular potassium, decrease in the cellular level of key metabolites (ATP, glucose-6-phosphate and pyruvate) and fragility of protoplasts following the action of cell wall-degrading enzymes.
Nevertheless, cell growth resumes after a short lag phase (2–4 days) with an actual 70–100% cell survival, thus indicating that the observed damage is not lethal and can be repaired in a short time. 相似文献
Nevertheless, cell growth resumes after a short lag phase (2–4 days) with an actual 70–100% cell survival, thus indicating that the observed damage is not lethal and can be repaired in a short time. 相似文献