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排序方式: 共有167条查询结果,搜索用时 31 毫秒
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2.
Peter R. Minchin 《Plant Ecology》1987,69(1-3):89-107
3.
Cloning, sequencing and analysis of the structural gene and regulatory region of the Pseudomonas aeruginosa chromosomal ampC beta-lactamase. 总被引:7,自引:0,他引:7 下载免费PDF全文
The chromosomal gene from Pseudomonas aeruginosa encoding beta-lactamase has been cloned, and the sequence determined and compared with corresponding sequences of beta-lactamases from members of the enterobacteriaceae. Upstream of the beta-lactamase gene is an open reading frame which we postulate encodes a regulatory protein, AmpR. We identified a helix-turn-helix region in AmpR and a putative AmpR-binding site. 相似文献
4.
Involvement of Activated Oxygen in Nitrate-Induced Senescence of Pea Root Nodules 总被引:8,自引:1,他引:7 下载免费PDF全文
Escuredo PR Minchin FR Gogorcena Y Iturbe-Ormaetxe I Klucas RV Becana M 《Plant physiology》1996,110(4):1187-1195
The effect of short-term nitrate application (10 mM, 0-4 d) on nitrogenase (N2ase) activity, antioxidant defenses, and related parameters was investigated in pea (Pisum sativum L. cv Frilene) nodules. The response of nodules to nitrate comprised two stages. In the first stage (0-2 d), there were major decreases in N2ase activity and N2ase-linked respiration and concomitant increases in carbon cost of N2ase and oxygen diffusion resistance of nodules. There was no apparent oxidative damage, and the decline in N2ase activity was, to a certain extent, reversible. The second stage (>2 d) was typical of a senescent, essentially irreversible process. It was characterized by moderate increases in oxidized proteins and catalytic Fe and by major decreases in antioxidant enzymes and metabolites. The restriction in oxygen supply to bacteroids may explain the initial decline in N2ase activity. The decrease in antioxidant protection is not involved in this process and is not specifically caused by nitrate, since it also occurs with drought stress. However, comparison of nitrate- and drought-induced senescence shows an important difference: there is no lipid degradation or lipid peroxide accumulation with nitrate, indicating that lipid peroxidation is not necessarily involved in nodule senescence. 相似文献
5.
Xavier Khawaja Non Evans Yvonne Reilly Christine Ennis Michael C. W. Minchin 《Journal of neurochemistry》1995,64(6):2716-2726
Abstract: The specific binding of [3H]WAY-100635 {N-[2-[4-(2-[O-methyl-3H]methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexane carboxamide trihydrochloride} to rat hippocampal membrane preparations was time, temperature, and tissue concentration dependent. The rates of [3H]WAY-100635 association (k+1 = 0.069 ± 0.015 nM?1 min?1) and dissociation (k?1 = 0.023 ± 0.001 min?1) followed monoexponential kinetics. Saturation binding isotherms of [3H]WAY-100635 exhibited a single class of recognition site with an affinity of 0.37 ± 0.051 nM and a maximal binding capacity (Bmax) of 312 ± 12 fmol/mg of protein. The maximal number of binding sites labelled by [3H]WAY-100635 was ~36% higher compared with that of 8-hydroxy-2-(di-n-[3H]-propylamino)tetralin ([3H]8-OH-DPAT). The binding affinity of [3H]WAY-100635 was significantly lowered by the divalent cations CaCl2 (2.5-fold; p < 0.02) and MnCl2 (3.6-fold; p < 0.05), with no effect on Bmax. Guanyl nucleotides failed to influence the KD and Bmax parameters of [3H]WAY-100635 binding to 5-HT1A receptors. The pharmacological binding profile of [3H]WAY-100635 was closely correlated with that of [3H]8-OH-DPAT, which is consistent with the labelling of 5-hydroxytryptamine1A (5-HT1A) sites in rat hippocampus. [3H]WAY-100635 competition curves with 5-HT1A agonists and partial agonists were best resolved into high- and low-affinity binding components, whereas antagonists were best described by a one-site binding model. In the presence of 50 µM guanosine 5′-O-(3-thiotriphosphate) (GTPγS), competition curves for the antagonists remained unaltered, whereas the agonist and partial agonist curves were shifted to the right, reflecting an influence of G protein coupling on agonist versus antagonist binding to the 5-HT1A receptor. However, a residual (16 ± 2%) high-affinity agonist binding component was still apparent in the presence of GTPγS, indicating the existence of GTP-insensitive sites. 相似文献
6.
Possible causes of the physiological decline in soybean nitrogen fixation in the presence of nitrate 总被引:2,自引:2,他引:0
Arrese-Igor Cesar; Minchin Frank R.; Gordon Anthony J.; Nath Amarjit K. 《Journal of experimental botany》1997,48(4):905-913
Nodulated soybean plants (Glycine max (L.) Merr. cv. Clarke)were supplied with 10 mol m-3 nitrate at the vegetative stage.This treatment caused a rapid decline in nitrogen fixation (acetylenereduction) activity and a consequent decline in ureides in thexylem sap. However, there was virtually no effect on the nitrogenasecomplex, according to Western blots against components 1 and2. The effect on nitrogen fixation was matched by a decreasein nitrogenase-linked respiration and increases in nodule oxygendiffusion resistance and the carbon cost of nitrogen fixation.The addition of nitrate had little effect on protein contentfrom either nodule plant or bacteroid fractions. Activitiesof nitrate reductase (NR) and nitrite reductase (NiR) from eitherthe plant fraction or the bacteroids were affected in differentways during 8 d of supply. Nodule plant NR and bacteroid NiR were not affected. However,nodule plant NiR increased 5-fold within 2 d of supplying Bacteroid NR only increased after6 d. These results could be interpreted in terms of a restrictednitrate access into the infected region of nodules. However,denitrification was detected within 2 d of nitrate supply insoybean nodules. The results are discussed in relation to possiblecauses of the nitrate-induced decline in nitrogenase activity. Key words: Glycine max, nitrate, nitrogen fixation, nodules 相似文献
7.
M. C. W. Minchin 《Journal of neurochemistry》1979,32(5):1519-1524
Abstract— [14 C]Nipecotic acid was accumulated in isolated desheathed rat dorsal root ganglia by a saturable process with K m = 48.8 μ m and V max = 2.2 nmol/g/min. The concentration of l -2.4-diamino-butyric acid required to inhibit the uptake of nipecotic acid by 50% was three times the concentration of β-alanine required to do the same. Light microscopic autoradiography indicated that the sites of uptake of [14 C]nipecotic acid were principally confined to satellite glial cells. It is concluded that nipecotic acid is transported by the GABA uptake system in glia but that it has less affinity for this system than GABA. 相似文献
8.
The uptake of intracellular putrescine and spermidine was examined in B16 melanoma cells. It was found that difluoromethylornithine preferentially induced putrescine transport (28-fold) compared to that for spermidine (3.5-fold). Putrescine uptake was partially Na+ dependent, whereas spermidine uptake was not. Inhibition studies with the two polyamines showed that putrescine was a poor competitive inhibitor of spermidine uptake, exhibiting a Ki of 69-75 microM, whereas the estimated Km for putrescine uptake was only 5.36 microM. By contrast, spermidine inhibition of putrescine transport produced a non-linear Eadie-Scatchard plot suggesting that putrescine was taken up by a spermidine-sensitive and a spermidine-insensitive process. The estimated spermidine Ki for inhibition of the spermidine-sensitive process was 0.125 microM. Using a series of polypyridinium quaternary salts to inhibit transport, no correlation between inhibition of putrescine uptake and inhibition of spermidine uptake was seen. Finally, the photoaffinity label, 1,12-di(N5-azido-2-nitrobenzoyl)spermine selectively inactivated the putrescine transporter(s) without affecting spermidine uptake. From these observations, it was concluded that multiple polyamine transporters are present on B16 melanoma cells and that separate, distinct transporter(s) account for the uptake of putrescine and spermidine in this cell-line following induction with difluoromethylornithine. The present of different transporters for the two polyamines indicates that expression of uptake activity for putrescine and spermidine may be under separate cellular control. 相似文献
9.
Stephen Rawsthorne Frank R. Minchin Rodney J. Summerfield Claire Cookson James Coombs 《Phytochemistry》1980,19(3):341-355
The literature concerning the metabolism of carbon compounds during the reduction, assimilation and translocation of nitrogen in root nodules of leguminous plants is reviewed. The reduction of dinitrogen requires an energy source (ATP) and a reluctant which are both supplied by respiratory catabolism of carbohydrates produced by the host plant. Photosynthates are also required to generate the carbon skeletons for amino acid or urcide synthesis during the assimilation of ammonia produced by the bacteria within the nodule tissue. Competition for photosynthates occurs between the bacteroids, nodule tissue and the various vegetative and reproductive sinks in the host plant. The nature of carbon compounds involved in these processes, their routes of metabolism, the mechanisms of control and the partitioning of metabolises between the various sites of utilization are only poorly understood. It is apparent that dinitrogen is reduced to ammonia in the bacteroids. Both fast- and slow-growing strains of Rhizobium possess the Entner-Doudoroff pathway of glucose catabolism, and some, if not all, enzymes of the Emden-Meyerhof pathway. Some bacterial cultures also metabolize carbon through the ketogluconate pathway but only the fast-growing strains of cultured rhizobia possess the key enzyme of the pentose phosphate pathway (6-phosphogluconate dehydrogenase). The host cells are thought to contain the complete Emden-Meyerhof pathway and tricarboxylic acid cycle, which provides the carbon skeletons for assimilation of the ammonia, formed by the bacteroids, into α-amino acids. A pathway of anapleurotic carbon conservation, operative in the host cells, synthesizes oxaloacetic acid through β-carboxylation of phosphoenol pyruvate. This process could be important in the recapture and assimilation of respired CO2 in the rhizosphere. The main route of assimilation of ammonia produced by the bacteroids would appear to be via the glutamine synthetase-glutamate synthase pathway in the host cells. However, glutamate dehydrogenase may also be involved in ammonia assimilation. These enzymes also occur in in vitro cultures of Rhizobium and in bacteroids where they presumably participate in the synthesis of amino acids for growth of the bacteria or bacteroids. Nitrogen assimilated into glutamine or glutamate is exported from the nodules in a variety of forms, which include asparagine, glutamine, aspartate, homoserine and allantoates, in proportions which depend on the legume species. Studies on regulation of the overall process have focussed on expression of bacteroid genes and on the control of enzyme activity, at the level of nitrogenase and enzymes of nitrogen assimilation in particular. However, due to the wide range of experimental techniques, environmental conditions and plant species which have been used, no clear conclusions can yet be drawn. The pathways of carbon flow in nitrogen metabolism, particularly in relation to the synthesis of ureides and the regulation of carbon metabolism, remain key areas for future research in symbiotic nitrogen fixation. 相似文献
10.