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21.
Tandem duplication and divergence of a sea urchin protein belonging to the troponin C superfamily 总被引:1,自引:0,他引:1
M Q Xiang P A Bédard G Wessel M Filion B P Brandhorst W H Klein 《The Journal of biological chemistry》1988,263(32):17173-17180
The Spec1 and Spec2 proteins of the sea urchin Strongylocentrotus purpuratus are related to calmodulin, troponin C, and myosin light chains by sequence similarity in their four calcium binding domains. These domains, the EF-hands, are distinct helix-loop-helix structures of about 40 amino acids. The Spec1 and Spec2 genes are expressed specifically in aboral ectoderm cells of the developing embryo; however, the function of the Spec proteins in these cells is unknown. To find conserved regions of the proteins that might be important for structure and function, Spec homologues from Lytechinus pictus, a distantly related sea urchin, were sought. L. pictus embryos do not synthesize detectable amounts of the 14,000-17,000-Da Spec proteins as determined by two-dimensional gel electro-phoresis, but do synthesize three 34,000-Da proteins that cross-react with Spec1 antibodies and display a similar ontogenetic pattern of expression. cDNA clones were isolated by hybridization to a synthetic oligonucleotide corresponding to the EF-hand. One clone, LpS1, encodes an mRNA with developmental properties like those of the S. purpuratus Spec mRNAs. However, LpS1 contains an open reading frame for a protein of 34,000 Da rather than 17,000 Da, and antibodies raised against part of the LpS1 reading frame demonstrate that LpS1 encodes a 34,000-Da protein in L. pictus embryos. The sequence of LpS1 reveals the presence of eight EF-hand domains, which share structural homology with the Spec1 or Spec2 EF-hands; however, little else in the protein sequence is conserved. The results support the hypothesis that the LpS1 gene arose from a duplication of an ancestral Spec gene and that the overall structural features of the Spec family of proteins are more conserved than the amino acid sequences. 相似文献
22.
Construction and expression of nonsense suppressor tRNAs which function in plant cells 总被引:3,自引:0,他引:3
Scott Franklin Tsai Yun Lin William R. Folk 《The Plant journal : for cell and molecular biology》1992,2(4):583-588
An Arabidopsis thaliana L. DNA containing the tRNA(TrpUGG) gene was isolated and altered to encode the amber suppressor tRNA(TrpUAG) or the ochre suppressor tRNA(TrpUAA). These DNAs were electroporated into carrot protoplasts and tRNA expression was demonstrated by the translational suppression of amber and ochre nonsense mutations in the chloramphenicol acetyltransferase (CAT) reporter gene. DNAs encoding tRNA(TrpUAG) and tRNA(TrpUAA) nonsense suppressor tRNAs caused suppression of their cognate nonsense codons in CAT mRNAs, with the tRNA(TrpUAG) gene exhibiting the greater suppression under optimal conditions for expression of CAT. The development of these translational suppressors which function in plant cells facilitates the study of plant tRNA gene expression and will make possible the manipulation of plant protein structure and function. 相似文献
23.
蓝藻型富营养湖泊藻量的昼夜变化节律 总被引:3,自引:0,他引:3
杭州西湖为蓝藻型富营养湖泊,根据1980年9月及11月二次昼夜分层采样调查,该湖浮游藻在一昼夜中有二次上下垂直移位,使近表层藻量形成规则或不规则的双峰型昼夜变化曲线,双峰分别出现在日照开始与日落后2h左右,认为昼夜光暗交替与其昼夜变化有一定相关关系,同时,双峰的形成与蓝藻门优势藻种对光照强度的适应性能相关。文中对其优势藻种的浮沉与日照关系作了讨论。 相似文献
24.
毒黄素对黄嘌呤氧化酶作用的影响 总被引:1,自引:0,他引:1
利用从椰毒假单胞菌(Pseudomona cocovenenans)中所分离提取的毒黄素(toxoflavin)对黄嘌呤氧化酶(EC.1、2 3、2)作用的动力学试验表明,毒黄素是此酶的非必需激活剂,而且对以次黄嘌呤为底物的反应的激活作用明显高于以黄嘌呤为底物的反应。此激活作用属于部分混合型。这一结果为探寻毒黄素对人体的致毒机理提供了一条重要线索。 相似文献
25.
为了了解外周神经损伤对体感皮层分域组构的影响,在成年大鼠上观察了切断坐骨神经(SC)前、即刻和切断后数周内后爪皮层代表区的改变。在盐酸氯胺酮麻醉下,用微电极记录后爪皮肤轻触刺激在对侧体感皮层工区诱发的多单位反应,得出后爪的皮层代表区图。在16例中,8例大鼠观察了切断SC的即时效应。结果表明,不但SC代表区丧失皮肤反应性,原隐神经(SA)代表区的皮肤反应性也明显下降或消失,同时神经元自发活动也明显减弱。另8例大鼠在切断后数周内做了1~3次重复测定。在最初几天,原SA代表区范围内多数记录点的皮肤反应性仍未恢复,但在原SC代表区内,一些记录点转而对SA皮肤轻触刺激起反应。在随后数周内SA代表区进行性地扩张,占领了大部分原SC代表区。这一结果说明成年大鼠外周神经损伤可导致体感皮层发生显著的重组改变。 相似文献
26.
通过DEAE-SephadexA-50,DEAE-SepharoseCL-6B,MonoQ (FPLC)三步离子交换柱层析,纯化得到一新的纤维蛋白原溶酶,在碱性聚丙烯酰胺凝胶电泳和SDS-聚丙烯酰胺凝胶电泳上均呈单一的蛋白带。分子量为2600,等电点pl4.7;它是一个糖蛋白,含糖量6.4%,其中中性糖0.3%,已糖胺4.9%,唾液酸1.2%。烙铁头蛇毒纤维蛋白原溶酶TMVFg由187个氨基酸组成,含有较高的酸性氨基酸,此外甘氨酸含量也较高。TMVFg热稳定性强,而酸不稳定,在280 nm处具有典型的蛋白吸收峰,在无离子水中紫外消光系数E0.1%/280 nm=1.558。纯化的TMVFg具有较强的精氨酸酯酶活力,对苯甲酰-L-精氨酸乙酯(BAEE)的Km值为1.4×10[-3]M。TMVFg的活性受苯甲基丹磺酰氟(PMSF)抑制;乙二胺四乙酸(EDTA)对活性无影响。TMVFg不能使纤维蛋白原凝固,但能水解纤维蛋白原α、β链。纤溶实验表明TMVFg具有激活纤溶作用。纯化的烙铁头蛇毒纤维蛋白原溶酶对酪蛋白无作用,无出血活性,因而与凝血酶样酶、出血毒素及β-纤维蛋白原溶酶(OUYANG et al.,1977)明显不同。 相似文献
27.
28.
S W Melanson C H Yun M L Pezzementi L Pezzementi 《Comp. Biochem. Physiol. C, Comp. Pharmacol. Toxicol.》1985,81(1):87-96
The acetylcholinesterase activity of the fruit fly, Drosophila melanogaster, was characterized biochemically. The activity is associated with a glycoprotein which is divided between a detergent-extractable membrane-bound fraction and a soluble fraction. The acetylcholinesterase activity is concentrated in the head of the insect. Through pharmacological methods, greater than 95% of the cholinesterase is judged to be true acetylcholinesterase, and not pseudocholinesterase. As expected for an acetylcholinesterase, the enzyme has a high affinity for acetylthiocholine and is inhibited by excess concentrations of acetylthiocholine. The soluble enzyme is found predominantly as a 7.8 S form; a smaller amount of an approximately 6 S form is also present, and a greater than or equal to 14 S form may exist. The detergent-solubilized acetylcholinesterase has a sedimentation coefficient of 7.5 S in the presence of detergent. The thermal inactivation rates for the soluble and the membrane bound enzymes are markedly different. 相似文献
29.
Immature rats (aged 28 days) were injected with 4, 20, or 40 IU pregnant mare serum gonadotropin (PMSG) and sacrificed every 6 or 12 hr. Control rats (4 IU) ovulated between 60 and 72 hr, whereas rats given superovulatory doses of PMSG (20 and 40 IU) ovulated between 24 and 72 hr. The oocyte count from the superovulated rats increased slightly between 24 and 36 hr and markedly between 48 and 72 hr. Degenerated oocytes were recovered 48 and 36 hr after administration of 20 and 40 IU PMSG, respectively. Thereafter, the proportion of degenerated oocytes was dose dependent and reached a maximum at 72 (30.9%, 20 IU) and 60 hr (61.0%, 40 IU). 17β-estradiol content of the superovulated ovaries increased significantly (P < 0.01) from 36 hr and was maximal at 60 (20 IU) or 54 hr (40 IU), when compared to the control regimen. Administration of 40 IU PMSG resulted in a biphasic increase of progesterone content with the peaks at 36 and 60 hr. Androgen content of the superovulated ovaries was lower than control levels during the first 36 hr but was significantly (P < 0.01) higher thereafter. The results suggest that these alterations in the steroid response (particularly androgens) from 36 hr onward following superovulation may be responsible for the coincidental occurrence of abnormal oocytes, possibly by disturbing the specific intrafollicular steroid environment essential for complete maturation. In addition, oocyte aging that is due to earlier activation by the exogenous luteinizing hormone activity may be a contributing factor. 相似文献
30.