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991.
992.
Induction of sialic acid 9-O-acetylation by diverse gene products: implications for the expression cloning of sialic acid O- acetyltransferases 总被引:1,自引:0,他引:1
Sialic acids can be modified by O-acetyl esters at the 7- and/or 9-
position, altering recognition by antibodies, lectins and viruses. 9(7)-
O-acetylation is mediated by a sialic acid-specific O- acetyltransferase,
which has proven difficult to purify. Two groups have recently isolated
cDNAs possibly encoding this enzyme, by expression cloning of human
melanoma libraries in COS cells expressing the substrate ganglioside GD3.
Pursuing a similar approach, we have isolated additional clones that can
induce 9-O-acetylation. One clone present in a melanoma library encodes a
fusion protein between a bacterial tetracycline resistance gene repressor
and a sequence reported to be part of the P3 plasmid. Expression of the
open reading frame is necessary for inducing 9-O-acetylation, indicating
that this is not a reaction to the introduction of bacterial DNA. Another
clone from a rat liver cDNA library induced 9-O-acetylation on COS cells
expressing alpha2-6-linked sialic acids, and encodes an open reading frame
identical to the Vitamin D binding protein. However, truncation at the 5'
end eliminates the amino-terminal hydrophobic signal sequence, predicting
cytosolic hyperexpression of a truncated protein. Thus, diverse types of
cDNAs can indirectly induce sialic acid 9-O- acetylation in the COS cell
system, raising the possibility that the real enzyme may be composed of
multiple subunits which would not be amenable to expression cloning.
Importantly, the cDNAs we isolated are highly specific in their ability to
induce 9-O-acetylation either on alpha2-6-linked sialic acids of
glycoproteins (truncated vitamin D binding protein) or on the
alpha2-8-linked sialic acids of gangliosides (Tetrfusion protein). These
data confirm our prior suggestion that a family of O-acetyltransferases
with distinctive substrate specificities exists in mammalian systems.
相似文献
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应用免疫组织化学技术,观察了30只Wistar大鼠脑血管颈内动脉系肾上腺素能神经的起始核团。正常组脑血管颈内动脉系均可见棕褐色的免疫反应阳性纤维。手术1组作一侧颈上神经节切除术,同侧大脑前动脉、大脑中动脉和大脑后动脉的阳性纤维较正常组减少约2/3,对侧同部位动脉的阳性纤维约减少1/3;手术Ⅱ组作双侧颈上神经节切除术,双侧大脑前动脉、大脑中动脉和大脑后动脉的阳性纤维基本消失。结果提示:脑血管一侧颈内动脉系的肾上腺素能神经纤维起源于双侧颈上神经节。讨论了交感神经对脑血管可能的作用。 相似文献
997.
本文以中季稻区稻田主要害虫稻飞虱、稻纵卷叶螟和捕食天敌蜘蛛的田间系统调查资料为基础,以害虫—天敌—农药系统为研究对象,应用害虫管理系统工程的原理,处理害虫、捕食天敌与农药三者之间的关系。建立了稻纵叶螟—蜘蛛—甲胺磷和稻飞虱—蜘蛛—甲胺磷两系统优化管理模型,绘制了它们的优化反馈控制策略图,利用微机对系统进行最优监控。使用时输入当前田间害虫与天敌数量,就可对系统作出即时的预测和最优决策。该策略确立的控制害虫的最优性能指标,是使害虫对农作物的为害所造成的损失与防治费用之和最小,并且使害虫和天敌的数量处于系统平衡状态。文中比较分析了该策略与基于经济阈值的常规害虫管理策略,指出了新策略在害虫综合治理中对天敌数量进行控制和管理的作用及其意义。 相似文献
998.
真核细胞基因组DNA的甲基化主要发生在CpG二核苷酸对的胞嘧啶环上(m5C)[1,2].在真核细胞基因组DNA内,约70%的CpG位点发生了甲基化.CpG位点在基因组DNA内并不是均匀分布的,多数聚集在一些基因的5’端.大量的实验证据表明,真核基因5... 相似文献
999.
Yan Shi Wei Luo Wei-Xi Tian Tong Zhang Hai-Meng Zhou 《The international journal of biochemistry & cell biology》1998,30(12):1319-1330
Fatty acid synthase is an important enzyme participating in energy metabolism in vivo. The inactivation and conformational changes of the multifunctional fatty acid synthase from chicken liver in SDS solutions have been studied. The results show that the denaturation of this multifunctional enzyme by SDS occurred in three stages. At low concentrations of SDS (less than 0.15 mM) the enzyme was completely inactivated with regard to the overall reaction. For each component of the enzyme, the loss of activity occurred at higher concentrations of SDS. Significant conformational changes (as indicated by the changes of the intrinsic fluorescence emission and the ultraviolet difference spectra) occurred at higher concentrations of SDS. Increasing the SDS concentration caused only slight changes of the CD spectra, indicating that SDS had no significant effect on the secondary structure of the enzyme. The results suggest that the active sites of the multifunctional fatty acid synthase display more conformational flexibility than the enzyme molecule as a whole. 相似文献
1000.
Abstract Investigations on the pest-natural enemy-insecticide system, including rice leaf roller-spider-tamaron and planthopper-spider-tamaron system, were carried out in the paddy fields in middle season rice cropping region. The relationship among insect pest, natural enemy and insecticide were studied based on the principle of the pest management system engineering. The optimal management models of the two systems were developed. Their diagrams of optimal feedback control strategy were contoured for computer monitoring of the pest-natural enemy-insecticide system. The population densities of pest and natural enemy in the future could be forecasted and the optimal strategy could be made when the current field densities of pest and natural enemy were input into the computer. The optimal performance index, which is a combination of the total cost of using the chemical and the total cost of pest damage to crops, for pest control is minimized. The objective of the system management is to drive the state of the system towards a beneficial equilibrium of the system generally. A comparison of the new IPM strategy with the ordinary strategy based on a single economic threshold is conducted in this paper. The optimal control strategies suggest that both pest and natural enemy populations should be controlled in the integrated pest management. 相似文献