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31.
The N-terminal signal sequence of glucitol pcrmease of Escherichia Coli (Gut22) and its analogue (Gut22Ana) were synthesized. The analogue had a Pro residue substituting for the His at the 7th position of Gut22 and a Val residue substituting for the Glu at the 10th position. The intrinsic fluorescence emission spectra indicated that the binding of Gut22 with lipid bilayer was much stronger than that of Gut22Ana. The leakage experiments with calcein-loaded liposomes showed that Gut22 strongly perturbed lipid bilayers while Gut22Ana did not. The apparent partition constant of Gut22 for partitioning into phosphatidylserine/phosphatidylcholine bilayers was measured; the effect of membrane potential on the interaction of Gut22 with lipid bilayers was studied and the conformation changes of Gut22 and Gut22Ana upon interacting with liposomes were studied by the method of circular dichroism analysis. 相似文献
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34.
Temporal and spatial variations in the oxygen-18 content of leaf water in different plant species 总被引:7,自引:3,他引:4
Temporal variations in the δ18 oxygen (δ18O) content of water transpired by leaves during a simulated diurnal cycle fluctuated around the δ18O content of the source water. Reconstructed variations in the δ18O values of leaf water differed markedly from those predicted by conventional models. Even when transpiring leaves were maintained under constant conditions for at least 3 h, strict isotopic steady-state conditions of leaf water (equality of the 18O/16O ratios in the input and transpired water) were rarely attained in a variety of plant species (Citrus reticu-lata, Citrus paradisi, Gossypium hirsutum, Helianthus annuns, Musa musaceae and Nicotinia tabacum). Isotopic analysis of water transpired by leaves indicated that leaves approach the isotopic steady state in two stages. The first stage takes 10 to 35 min (with a rate of change of about 3–3%h?1), while in the second stage further approach to the isotopic steady state is asymptotic (with a rate of change of about 0–4% h?1), and under conditions of low transpiration leaves can last for many hours. Substantial spatial isotopic heterogeneity was maintained even when leaves were at or near isotopic steady state. An underlying pattern in this isotopic heterogeneity is often discerned with increasing 18O/16O ratios from base to tip, and from the centre to the edges of the leaves. It is also shown that tissue water along these spatial isotopic gradients, as well as the average leaf water, can have 18O/16O ratios both lower and higher than those predicted by the conventional Craig and Gordon model. We concluded, first, that at any given time during the diurnal cycle of relative humidity the attainment of an isotopic steady state in leaf water cannot be assumed a priori and, secondly, that the isotopic enrichment pattern of leaf water reflects gradual enrichment along the water-flow pathway (e.g. as in a string of pools), rather than a single-step enrichment from source water, as is normally assumed. 相似文献
35.
本文记述中国弯茎叶蝉属FlexocerusKnohetFang1新种,吴萸弯茎叶蝉Flexocerusevodianussp.nov.,新种外形特征与弯茎叶蝉FlexocerusflexureuskuohetFang相似。模式标本保存在贵州农学院。 相似文献
36.
中国厕蝇属一新种(双翅目:厕蝇科) 总被引:1,自引:0,他引:1
本文记述采自山西省的厕蝇属Fannia R.-D.,1830一新种。录属于瘤胫厕蝇群xcalaris-group,胸刺厕蝇亚群fuscula-subgroup,命名为突尾厕蝇Fannia processicauda sp.nov.,新种模式标本保存于山西省大同市地方病防治所。 相似文献
37.
神经生长因子结构与功能研究进展 总被引:2,自引:0,他引:2
神经生长因子(NGF)是神经营养因子家族的典型代表, 它控制着脊椎动物周围和中枢神经系统中部分神经元的发育和存活.NGF的三维结构是以“胱氨酸结”和β折叠为基础,它以二聚体的形式结合细胞表面的受体从而发生生物学效应.参与这些反应的氨基酸残基已通过化学修饰和定点突变法加以确定,这有助于更进一步理解其结构与功能的关系. 相似文献
38.
银额果蝇自然群体分化过程中的细胞遗传学 总被引:3,自引:0,他引:3
对我国大陆银额果蝇的分布及其细胞遗传学进行了广泛的调查,发现了一种值得注意的新核型。该核型结构兼有早已认可的长、短两大类基本核型的特征,即核型中的两条同源4号染色体为1长1短型。含新核型的群体分布于我国大陆东南沿海一带的上海、福州、厦门和深圳。而且,这些自然群体内还出现“1长1短型”、“长型”和“短型”重叠并存的多态现象。跟踪研究表明,新核型具有不稳定的遗传性,能世代传递,它的频率随世代增长而降低,并不是突然消失。但是,在上海、福州群体内出现的“长型”至第十五代之后却全部消失。这种新核型大概是银额果蝇自然演化过程中的中间过渡核型,是该果蝇种群分化中的细胞遗传学变异的过渡表征 相似文献
39.
An efficient plasmid transformation system forS. mycarofaciens 1748 has been established. In order to determine the function of MKR gene in S.mycarofaciens 1748, the gene disruption experiment was carried out. For this purpose the plasmid pKC1139 was used. A recombinant strain
with white spore appeared, in contrast to the grey-colour spore of S.myarofaciens 1748. This suggested that homologous recombination between plasmidborne MKR gene sequence and the chromosome of S.mycarofaciens 1748 had occurred. A Southern hybridization experiment using a-32P-labelled MKR gene as probe indicated that the desired integration event had occurred in the recombinant. The result of gene
disruption showed that the alteration of this gene in the chromosome of S.mycarofaciens 1748 made sporulating colonies remain white instead of taking on the typical grey colour of sporulating wild type colonies,
suggesting that MKR gene is involved in the biosynthesis of a spore pigment. The recombinant strain was incubated with fermentation
medium optimised for midecamycin production. A TLC assay showed that the recombinant strain produced midecamycin in quantities
comparable to that ofS. mycarofaciens 1748. A pCN8B12 was a clone from genomic library of midecamycin producing strain which contained a 28-kb DNA insert. The
28-kb DNA fragment contained act I-homologous and act III-homologous regions. he PKS (act I-homologous) and MKR (act III-homologous)
genes that define spore pigment of midecamycin producing strain were Jocalized by restriction endonuclease digestion with
pCN8B12, indicating that they are separated by about 10 kb DNA. The polyketide synthase gene cluster of simila; organization
has not been reported yet.
Project supported by the National Natural Science Foundation of China. 相似文献
40.
本文记述采自江西的翼手恙螨属一新种,由毛翼手恙螨,新种Chiroptella curvisetosa sp.nov.,模型标本保存于江西医学院寄生虫学教研室。 相似文献