共查询到20条相似文献，搜索用时 375 毫秒
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<正>富氧养殖技术是水产健康养殖的重要方式。池塘底充式增氧技术可明显改善池塘养殖水环境,可广泛应用于南美白对虾和梭子蟹养殖,应用后的单产和经济效益递增显著,是一项节能、高效、深受广大养殖户欢迎的实用技术。 相似文献
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富氧养殖技术是水产健康养殖的重要方式。池塘底充式增氧技术可明显改善池塘养殖水环境，可广泛应用于南美白对虾和梭子蟹养殖。应用后的单产和经济效益递增显著，是一项节能、高效、深受广大养殖户欢迎的实用技术。 相似文献
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富氧养殖技术是水产健康养殖的重要方式。池塘底充式增氧技术可明显改善池塘养殖水环境的。可广泛应用于南美白对虾和梭子蟹养殖，应用后的单产和经济效益递增显著，是一项节能、高效及深受广大养殖户欢迎的实用技术。 相似文献
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<正>富氧养殖技术是水产健康养殖的重要方式。池塘底充式增氧技术可明显改善池塘养殖水环境的,可广泛应用于南美白对虾和梭子蟹养殖,应用后的单产和经济效益递增显著,是一项节能、高效及深受广大养殖户欢迎的实用技术。 相似文献
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Triggering of allostery in an enzyme by a point mutation: ornithine transcarbamoylase 总被引：5，自引：0，他引：5
The origin of allostery is an unanswered question in the evolution of complex regulatory proteins. Anabolic ornithine transcarbamoylase, a trimer of identical subunits, is not an allosteric enzyme per se. However, when the active-site residue arginine-106 of the Escherichia coli enzyme is replaced with a glycine through site-directed mutagenesis, the resultant mutant enzyme manifests substrate cooperativity that is absent in the wild-type enzyme. Both homotropic and heterotropic interactions occur in the mutant enzyme. The initial velocity saturation curves of the substrates, carbamoyl phosphate and L-ornithine, conform to the Hill equation. The observed cooperativity depends on substrate but not enzyme concentration. The finding underscores the possibility that a single mutation of the enzyme in the cell could turn transcarbamoylation into a regulatory junction in the biosynthesis of L-arginine and urea. 相似文献
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The activity of an enzyme system which readily converts estriol to 16-ketoestradiol is present only in the kidneys of mature female rats and is absent in the kidneys of male rats and immature rats of either sex. The full enzyme activity occurs in kidneys of rats of either sex at any stage of maturity after administration of estradiol for 2 weeks. The time course of the appearance and disappearance of the enzyme, the absence of detectable inhibitors and activators, and evaluation of cofactor requirements suggest that this may be an example of enzyme induction by the hormone. Furthermore, the enzyme activity itself represents a metabolic pathway for estriol metabolism whose potential quantitative significance has not heretofore been recognized. 相似文献
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The action of an enzyme essential for tryptophan biosynthesis is inhibited by tryptophan and also by an analog of tryptophan. Similarly, histidine and one of its analogs inhibit the action of an enzyme essential for histidine biosynthesis. A mutant resistant to the histidine analog produces an apparently altered enzyme which is insensitive to both the analog and histidine. 相似文献
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Purine overproduction in man associated with increased phosphoribosylpyrophosphate synthetase activity 总被引：13，自引：0，他引：13
In hemolyzates from red cells of two brothers with purine overproduction and gout, activity of phosphoribosylpyrophosphate synthetase is more than twofold greater than that measured in normal or other gouty individuals. The increased enzyme activity, which is also demonstrable in fibroblasts of the one patient tested, is associated with increased production of 5-phosphoribosyl-1-pyrophosphate by intact cells, an indication that the enzyme abnormality is the basis for the purine overproduction. This genetic abnormality is an example of an increased enzyme activity producing a disease state. 相似文献
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Enzyme defect associated with a sex-linked human neurological disorder and excessive purine synthesis 总被引：105，自引：0，他引：105
A sex-linked familial neurological disease consisting of cerebral palsy, mental retardation, choreoathetosis, and compulsive aggressive behavior is associated with a loss of an enzyme that participates in purine metabolism, namely, hypoxanthine-guanine phosphoribosyltransferase. The production of excessive uric acid in this disorder implies that the enzyme is involved in the normal regulation of purine biosynthesis. This is the first example of a relation between a specific enzyme defect and abnormal compulsive behavior. It is also the first enzyme defect in purine metabolism demonstrated in a neurological disease. 相似文献
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Evolution of malate dehydrogenase in birds 总被引：3，自引：0，他引：3
Heart extracts from over 100 species of birds were subjected to starch-gel electrophoresis at pH 7. The "supernatant" form of malate dehydrogenase, an enzyme present in every extract, was then located on the gels by a specific staining method. The mobility of this enzyme shows very little interspecific variation. Nearly all birds tested have a supernatant malate dehydrogenase that moves as fast as the chicken enzyme. Those species with an enzyme of unusual mobility are of taxonomic interest. For example, hummingbirds and swifts, which are usually considered as two suborders of Apodiformes, are unique among the birds tested in having an enzyme that moves 63 percent as fast as the chicken enzyme. This finding appears to confirm the unity of the Apodiformes, an order whose unity has long been open to question. Similarly all families tested in the shorebird order (Charadriiformes) are unique in having an enzyme that moves 55 percent as fast as the chicken enzyme. The unity of this order was also previously open to question. 相似文献
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选取5种植被恢复模式,研究了不同模式对土壤酶活性的影响以及土壤肥力与土壤酶活性的关系。结果表明,植被恢复后土壤蔗糖酶、过氧化氢酶和碱性磷酸酶活性相比光板地都有明显提高,顺序依次为酸角>小桐子>印楝;同种植被的土壤酶活性表现出根际大于非根际的特性;不同的植被恢复模式和种植方式对酶活性都有较大的影响,等高垄沟模式具有较好的保土保肥能力,创造了良好的微生物环境,增强了土壤酶活性;植被恢复模式下酶活性与土壤肥力之间的关系密切,特别是有机质、全氮与土壤蔗糖酶、过氧化氢酶和碱性磷酸酶的相关性较好。因此,用土壤酶活性来评价植被恢复的效果是可靠的。 相似文献
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The tryptophan hydroxylase activity in the rat midbrain decreases after adrenalectomy and is restored by treatment with corticosterone. Cycloheximide, adminiistered intracisternally, prevents the restoration of the enzyme activity by corticosterone. Cycloheximide administration to adrenalectomized rats resutlts in a further decrease in the enzyme activity. an indication that the enzyme has a rapid turnover even in the absence of corticosterone. 相似文献
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Regulation of an enzyme by phosphorylation at the active site 总被引：22，自引：0，他引：22
J H Hurley A M Dean J L Sohl D E Koshland R M Stroud 《Science (New York, N.Y.)》1990,249(4972):1012-1016
The isocitrate dehydrogenase of Escherichia coli is an example of a ubiquitous class of enzymes that are regulated by covalent modification. In the three-dimensional structure of the enzyme-substrate complex, isocitrate forms a hydrogen bond with Ser113, the site of regulatory phosphorylation. The structures of Asp113 and Glu113 mutants, which mimic the inactivation of the enzyme by phosphorylation, show minimal conformational changes from wild type, as in the phosphorylated enzyme. Calculations based on observed structures suggest that the change in electrostatic potential when a negative charge is introduced either by phosporylation or site-directed mutagenesis is sufficient to inactivate the enzyme. Thus, direct interaction at a ligand binding site is an alternative mechanism to induced conformational changes from an allosteric site in the regulation of protein activity by phosphorylation. 相似文献
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Dopamine-beta- hydroxylase is an enzyme that is localized to catecholamine-containing vesicles in sympathetic nerves and the adrenal medulla, and is also found in the serum. Treatment of rats with 6-hydroxydopamine, a drug which destroys sympathetic nerve terminals, leads to a decrease in serum dopamine-beta-hydroxylase activity. The decrease is not due to an effect on the adrenal medulla or to an increase in circulating inhibitor or inhibitors of enzyme. These data represent evidence that at least a portion of the circulating dopamine-beta-hydroxylase activity arises from sympathetic nerve terminals. 相似文献