共查询到20条相似文献,搜索用时 15 毫秒
1.
Defense in thrips: forbidding fruitiness of a lactone 总被引:1,自引:0,他引:1
Expulsion of anal fluid from the upturned abdomen was demonstrated to serve a defensive function in the thrips Bagnalliella yuccae. An allomone in the anal exudate was identified as gamma-decalactone, a fruity-smelling compound that repelled potential predators. Chemical defenses may contribute to the ability of thrips to maintain large aggregations. 相似文献
2.
克氏原螯虾原肌球蛋白的纯化及过敏原性分析 总被引:1,自引:0,他引:1
以13份甲壳类动物过敏患者血清的Western—blotting分析,确定克氏原螯虾主要过敏原为36ku蛋白质.通过盐析、等电点沉淀及热处理等方法纯化该蛋白质,以兔抗拟穴青蟹原肌球蛋白(Tropo-myosin,TM)多克隆抗体的Western—blotting分析,确定该蛋白质为TM.同源性分析表明,克氏原螯虾TM与南美白对虾TM、拟穴青蟹的氨基酸序列相似性较高(〉90%).酶切位点预测显示,它分别有49个胰蛋白酶和6个胰凝乳蛋白酶的酶切位点.模拟胃肠液消化实验结果显示,纯化TM不易被胃蛋白酶降解,易于被胰蛋白酶和胰凝乳蛋白酶降解,进一步的Western—blotting和抑制性ELISA分析结果显示,其消化产物仍具有一定的免疫活性.采用蒸煮处理可降低TM的消化稳定性及免疫活性,且蒸煮处理时间越长,效果越显著.说明。TM为克氏原螯虾主要过敏原.与其他甲壳娄动物TM的序列相似件较高. 相似文献
3.
CCAAT-enhancer binding protein: a component of a differentiation switch 总被引:95,自引:0,他引:95
The CCAAT-enhancer binding protein (C/EBP) has now been found to promote the terminal differentiation of adipocytes. During the normal course of adipogenesis, C/EBP expression is restricted to a terminal phase wherein proliferative growth is arrested, and specialized cell phenotype is first manifested. A conditional form of C/EBP was developed, making it feasible to test its capacity to regulate the differentiation of cultured adipocytes. Premature expression of C/EBP in adipoblasts caused a direct cessation of mitotic growth. Moreover, when abetted by the effects of three adipogenic hormones, C/EBP promoted terminal cell differentiation. Since C/EBP is expressed in a variety of tissues, it may have a fundamental role in regulating the balance between cell growth and differentiation in higher animals. 相似文献
4.
Tay-Sachs disease: generalized absence of a beta-D-N-acetylhexosaminidase component 总被引:55,自引:0,他引:55
Two hexosaminidase components, separable by starch-gel electrophoresis and possessing both beta-D-N-acetylglucosaminidase and beta-D-N-acetylgalactosaminidase activity, are present in human tissues. One of these, hexosaminidase component A, is absent in brain, liver, kidney, skin, cultured skin fibroblasts, blood plasma, and leukocytes from nine patients with Tay-Sachs disease. Hexosaminidase assay may facilitate the early diagnosis of individuals homozygous for Tay-Sachs disease. 相似文献
5.
Boffey PM 《Science (New York, N.Y.)》1976,193(4259):1224-1225
6.
Human synovial fluid: detection of a new component 总被引:2,自引:0,他引:2
J Sandson 《Science (New York, N.Y.)》1967,155(764):839-841
A new component has been detected in synovial fluid by the agar double-diffusion technique. This component is closely related immunologically to the proteinpolysaccharides of cartilage, and is the first probable degradation product of the cartilage matrix to be consistently identified in human synovial fluid. 相似文献
7.
Rhapidosomes of Saprospira grandis do not contain RNA that is highly methylated at the 2'-oxygen of the sugar residues. Neither is such an RNA associated with the particles as a contaminant. A cursory examination of the rhapidosomes of two other marine organisms gave similar results. 相似文献
8.
Selenium: biochemical role as a component of glutathione peroxidase 总被引:157,自引:0,他引:157
J T Rotruck A L Pope H E Ganther A B Swanson D G Hafeman W G Hoekstra 《Science (New York, N.Y.)》1973,179(73):588-590
When hemolyzates from erythrocytes of selenium-deficient rats were incubated in vitro in the presence of ascorbate or H(2)O(2), added glutathione failed to protect the hemoglobin from oxidative damage. This occurred because the erythrocytes were practically devoid of glutathione-peroxidase activity. Extensively purified preparations of glutathione peroxidase contained a large part of the (75)Se of erythrocytes labeled in vivo. Many of the nutritional effects of selenium can be explained by its role in glutathione peroxidase. 相似文献
9.
10.
Transmission electron microscope study of a chondritic interplanetary dust particle has revealed the presence of epsilon iron-nickel carbide, a low- temperature carbide previously encountered only in metallurgical studies. In these studies in-carbide was synthesized by carburization of iron or nickel grains in a stream of carbon monoxide or carbon monoxide plus hydrogen. Similar carburization of an iron-nickel metal in situ may have produced in-carbide during particle heating on atmospheric entry or in solar orbit. Alternatively, the epsilon-carbide may be a by-product of Fischer-Tropsch reactions in the solar nebula. Such reactions have been proposed as the mechanism of hydrocarbon formation in the early solar system. 相似文献
11.
The small magnetic field strength observed near Mars by Mariner IV suggests that protons from the solar wind may enter the Martian atmosphere and produce ionization in addition to that produced by ultraviolet light and x-rays. It is found that solar protons produce a thin ionized layer at a rate of the order of 3 x 10(3) per cubic centimeter per second at a depth corresponding to the F(1) region in the terrestrial atmosphere. Unless the effective recombinative coefficient is very large (greater than 10(-5) centimeter cubed per second) or unless unusual diffusion effects are present, this layer should have been detected by Mariner IV, and therefore must be present in one of the observed ionized regions. Because of its very compact shape, the subsidiary maximum near 95 kilometers discovered in the Mariner-IV occultation experiment may be the proton ionization peak. If so, the major 120-kilometer maximum is an F(2) layer. Distinction between photon and proton ionization regions can be made by microwave occultation experiments aboard planetary orbiters. 相似文献
12.
P E Sonnet 《Science (New York, N.Y.)》1967,156(783):1759-1760
2-Methyl-3-hexadecylpyrrolidine was synthesized. It has hemolytic activity as has solenamine, but it apparently does not have the insecticidal activity of the fire ant venom. As judged by gas chromatography, the structure is not a component of solenamine. 相似文献
13.
CDC25: a component of the RAS-adenylate cyclase pathway in Saccharomyces cerevisiae 总被引:46,自引:0,他引:46
L C Robinson J B Gibbs M S Marshall I S Sigal K Tatchell 《Science (New York, N.Y.)》1987,235(4793):1218-1221
The yeast Saccharomyces cerevisiae contains two functional homologues of the ras oncogene family, RAS1 and RAS2. These genes are required for growth, and all evidence indicates that this essential function is the activation of adenylate cyclase. In contrast, ras in mammalian cells does not appear to influence adenylate cyclase activity. To clarify the relation between ras function in yeast and in higher eukaryotes, and the role played by yeast RAS in growth control, it is necessary to identify functions acting upstream of RAS in the adenylate cyclase pathway. The evidence presented here indicates that CDC25, identified by conditional cell cycle arrest mutations, encodes such an upstream function. 相似文献
14.
Crystal and molecular structure of a phospholipid component: L-alpha-glycerophosphorylcholine cadmium chloride trihydrate 总被引:1,自引:0,他引:1
The structure of L-alpha-glycerophosphorylcholine cadmium chloride trihydrate has been determined by the conventional, single-crystal, x-ray diffraction technique. The phospholipid component displays the characteristic gauche conformation for the choline residue and the gauche-gauche conformation for the glycerol moiety. Therefore, a possible model for the structures of phospholipids is similar to that proposed by Finean. 相似文献
15.
Refractory periods were estimated for fibers of the hypothalamic substrate of brain stimulation reward. Two nonoverlapping populations were evident: a homogeneous fast population and a more heterogeneous slow population. Cholinergic blockade eliminated the contribution of the fast but not the slow fibers, while dopaminergic blockade reduced responding without significantly influencing either directly activated fiber population. These data indicate that the hypothalamic reward substrate is more complex than has been widely appreciated; it contains two or more parallel subsystems, and one of these subsystems has a cholinergic link. 相似文献
16.
Eclogitic diamonds have a large range of delta13C values, whereas peridotitic diamonds do not. Paired delta15N-delta13C-N variations in 40 eclogitic diamonds from the Jwaneng kimberlite in Botswana show that neither the influence of recycled biogenic carbon nor the global and primordial heterogeneity of mantle carbon are likely for the origin of the large delta13C range; the data instead support a fractionation process. It is proposed that carbonatitic mantle melts from which diamonds crystallize undergo different evolutions before diamond precipitation, when percolating through either a peridotite or an eclogite. These different evolutions, reflecting the presence or absence of olivine, can account for their respective delta13C distributions. 相似文献
17.
A Lacassagne N P Buu-Hoi F Zajdela P Jacquigmon M Mangane 《Science (New York, N.Y.)》1967,158(799):387-388
The title compound, which belongs to a new synthetic group of polycyclic lactones derived from isocoumarin, exhibits a remarkably high degree of carcinogenicity in situ when injected in mice. Cancer-inducing activity has also been found in similar isocoumarins, a family known to include many naturally occurring substances. 相似文献
18.
A crystalline hemolytic principle, shown to be a constituent of fire ant venom and having the properties of an amine, was isolated from crude extracts of whole ants. The chromatographic procedure of isolation is described, and a preliminary report is given about some properties of the substance. 相似文献
19.
GAARDER K 《Science (New York, N.Y.)》1960,132(3425):471-472
A transactional position suggests the hypothesis that there should be changes in the fine eye movements of a fixating subject if the fixated visual display is altered. It is shown that the mean saccadic eye movements are unequivocally different with different positions of the stimulus within the visual field. 相似文献