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61.
A mutant of Rhodobacter capsulatus was identified in which an operon encoding a binding-protein-dependent transporter was interrupted by Tn5 transposition. Cloning and sequence analysis of the wild-type operon revealed a four-gene cluster with similarities to genes encoding periplasmic binding proteins (BztA), integral membrane proteins (BztB and BztC), and ATP-binding proteins (BztD). To assess the function of this putative binding-protein-dependent transport system, a mutant was constructed in which most of the bztABCD operon was deleted and replaced by an antibiotic-resistance marker. The deletion mutant grew more slowly than the wild type in NH-free medium supplemented by glutamate, glutamine, aspartate or asparagine; it was resistant to toxic analogues of Glu, Asp, and Asn at concentrations that inhibited growth of the wild type; and it was defective in the uptake of Glu, Gin, and Asp. A complementing plasmid containing the wild-type copy of bztABCD was able to rescue all the mutant phenotypes. Taken together, these results indicate that the proteins encoded by bztABCD are active in the uptake of Glu, Gin, Asp, and Asn. In addition, competition experiments, in which the ability of each of the four amino acids to compete for the transport of one another was examined, demonstrated that all four substrates share at least one component of this transport system. 相似文献
62.
63.
凤眼莲(Eichhornia crassipes)的根分泌物中含有Met等多种氨基酸,其中Met、GABA、Gly、Ala、Asp、Ser、Val和Leu(10-7~10-2mol·L-1)均对凤眼莲的根际肠杆菌属F2(Enterobacter sp.F2)细菌有强烈的正趋化作用;Glu、Thr和His(10-7~10-3mol·L-1)也对该菌有一定的正趋化作用;而Lys、Cys、Arg、Tyr、Pro、Asn、Gln、Ile、Phe和Typ则对该菌表现出一定的负趋化作用.对细菌的正趋化作用存在一个趋化物的最适浓度范围.具有正趋化作用的氨基酸在凤眼莲根际的浓度都较高,而具有负趋化作用的浓度则较低,这正是凤眼莲与该根际细菌结合为根际微生态系统的原因之一. 相似文献
64.
65.
大鼠胼胝体内神经肽Y免疫反应阳性纤维的发育 总被引:1,自引:0,他引:1
本实验用免疫组织化学ABC法研究了大鼠胼胝体内神经肽Y免疫反应阳性(NPY-IR)纤维的生后发育。结果发现,许多NPY-IR纤维在大鼠出生时便存在于胼胝体内。NPY-IR胼胝体纤维的密度在生后1周内继续逐渐增高,在第2周内达到最高峰。之后,NPY-IR胼胝体纤维的密度逐渐下降,至第3周末时接近成年时的水平,即仅有少量NPY-IR纤维存在于胼胝体内。这些结果提示在大鼠早期生后发育过程中许多NPY-IR胼胝体纤维是暂时性的,其作用可能与大脑皮质的机能发育有关。 相似文献
66.
棉铃虫乙酰胆碱酯酶的底物专一性和发育期变化(英) 总被引:2,自引:0,他引:2
通过对河北省邯郸地区和山东省冠县的棉铃虫(Helicoverpa armigera H(?)bner)乙酰胆碱酯酶(AChE)研究,结果表明,棉铃虫乙酰胆碱酯酶对乙酰硫代胆碱(ATCh)和乙酰-β-甲基硫代胆碱(MeTCh)的比活力以及米氏常数(K_(?))值随其发育阶段呈有规律的变化,AChE比活力在幼虫期呈现两个高峰,一个在三龄,另一个在化蛹前;在蛹期AChE比活力没有明显的变化,而且比活力值比较低;到成虫期第4天有一个明显的高峰,比活力值高于其它任何虫态。K_(?)和最大反应速度(V_(max))的变化趋势基本上与比活力一致。棉铃虫AChE的K_(?)和比活力随其生长发育阶段的周期性变化对于指导用有机磷和氨基甲酸酯类杀虫药剂的化学防治具有重要的意义。不同地点采集到的棉铃虫AChE对AICh和MeTCh水解的活化能有所不同,邯郸地区的棉铃虫AChE水解MeTCh的活化能,蛹和成虫是幼虫期的3.9-4.3倍,而冠县棉铃虫水解MeTCh的活化能则变化不大。AChE水解ATCh的活化能,邯郸地区棉铃虫的AChE不同虫态间变化不大,冠县棉铃虫AChE,幼虫和成虫期约是蛹期的4倍。这说明不同生长发育时期,棉铃虫AChE对底物的水解所消耗的能量是不同的。棉铃虫幼虫AChE的最适反应条件是酶量以重量计为50-100mg,反应时间为10-20min,反应温度为35℃,反应体系的pH值为8.0。 相似文献
67.
用自制的氨基PEG化试剂rIL-2进行化学修饰,研究了试剂浓度,溶液pH,反应时间等与PEca-rIL-2产率及IL-2活性保持之间的关系,建立了一套获得稳定修饰度的PEG-rIL-2的方法。研究发现,反应时间跟修饰度关系不大;溶液pH对修饰度有一定的影响,中性pH以上反应都可进行;而试剂浓度直接决定修饰度的高低,过量越多,修饰度越高,而生物活性保留也越低;但低度修饰,对活性几乎没有影响,可保留活性在95%左右。 相似文献
68.
对我国首座核电站配套工程的抽水蓄能电站水库蓄水初期的浮游生物进行了调查。蓄水水库由上下两水库组成。两水库的浮游生物种类组成显著不同。上水库浮游植物共记录到30种(属),浮游动物12种(属);下水库浮游植物19种(属);浮游动物25种(属)。上下两水库浮游生物数量均较贫乏,表明浮游生物群落尚处于初期发育阶段,但在局部浅水处已出现小规模的蓝藻水花,认为是水库蓄水初期必然的结果 相似文献
69.
Immune Evasion by Helicobacter pylori: Gastric Spiral Bacteria Lack Surface Immunoglobulin Deposition and Reactivity with Homologous Antibodies 总被引:1,自引:0,他引:1
Peter E. Darwin Marcelo B. Sztein Qiao-Xi Zheng Stephen P. James George T. Fantry 《Helicobacter》1996,1(1):20-27
Background. Helicobacter pylori infection persists in the presence of potent serum and gastric mucosal anti-body responses against bacterial antigens. The aim of this article is to report on a study determine whether there is antibody deposition on H. pylori in vivo in the stomach of infected patients and whether gastric and cultured forms of H. pylori differ in their antibody reactivity.
Materials and Methods. Serum, gastric biopsies, and antral brushings were obtained from 10 patients having endoscopy. H. pylori was cultured from gastric biopsies. Bacterial samples were stained directly for immunoglobulin deposition and indirectly using rabbit antiurease serum or patient serum. Samples were examined by immunofluorescence microscopy and flow cytometry.
Results. Although spiral bacteria could be identified easily by acridine orange staining and antiurease staining of gastric brushings from H. pylori infected patients, gastric bacteria did not have detectable IgG or IgA present, and only one of five samples could be stained for IgG and IgA indirectly using patient serum. In contrast, cultured bacteria could be stained readily with homologous serum for IgG and IgA in the majority of cases. Low pH inhibited immunoglobulin reactivity with cultured H. pylori.
Conclusions. Gastric H. pylori may evade humoral defense owing to poor deposition of immunoglobulin in the gastric environment or failure to express surface antigens that are present on cultured forms of H. pylori. 相似文献
Materials and Methods. Serum, gastric biopsies, and antral brushings were obtained from 10 patients having endoscopy. H. pylori was cultured from gastric biopsies. Bacterial samples were stained directly for immunoglobulin deposition and indirectly using rabbit antiurease serum or patient serum. Samples were examined by immunofluorescence microscopy and flow cytometry.
Results. Although spiral bacteria could be identified easily by acridine orange staining and antiurease staining of gastric brushings from H. pylori infected patients, gastric bacteria did not have detectable IgG or IgA present, and only one of five samples could be stained for IgG and IgA indirectly using patient serum. In contrast, cultured bacteria could be stained readily with homologous serum for IgG and IgA in the majority of cases. Low pH inhibited immunoglobulin reactivity with cultured H. pylori.
Conclusions. Gastric H. pylori may evade humoral defense owing to poor deposition of immunoglobulin in the gastric environment or failure to express surface antigens that are present on cultured forms of H. pylori. 相似文献
70.
George T. Fantry Qiao-Xi Zheng Peter E. Darwin rew H. Rosenstein Stephen P. James 《Helicobacter》1996,1(2):98-106
Background Helicobacter pylori infection has been implicated strongly in the pathogenesis of gastritis, peptic ulcer disease, gastric adenocarcinoma, and gastric lymphoma, but the reasons for these widely different clinical outcomes are unknown. The aim of this study was to determine whether these differences could be due in part to mixed infection in the same individual, with bacteria having differences in pathogenic factors associated with ulcers.
Materials and Methods. The cagA gene of H. pylori was used to test for mixed infection because it is present in only some strains, and its presence has been associated with ulcers. Polymerase chain reaction (PCR) assays for the cagA gene were applied to H. pylori culture isolates and endoscopic gastric aspirates. Individual bacterial clones were tested for genetic similarity by random primer amplification and restriction endonuclease digestion of urease gene PCR products.
Results. The majority of H. pylori -positive patients had strongly cagA -positive culture isolates and endoscopic samples (62.5% and 69.6%, respectively). However, many of these patients had evidence of mixed infection with cagA negative and cagA positive strais in cultures isolates and endoscopic samples (25% and 17.4%, respectively). Mixed infection was found to be due to genetically unrelated strains in two patients in whom genetic analysis was performed.
Conclusion. Mixed infection with differences in substrain pathogenic factors might occur in H. pylori infection and might contribute to differences in clinical outcome. 相似文献
Materials and Methods. The cagA gene of H. pylori was used to test for mixed infection because it is present in only some strains, and its presence has been associated with ulcers. Polymerase chain reaction (PCR) assays for the cagA gene were applied to H. pylori culture isolates and endoscopic gastric aspirates. Individual bacterial clones were tested for genetic similarity by random primer amplification and restriction endonuclease digestion of urease gene PCR products.
Results. The majority of H. pylori -positive patients had strongly cagA -positive culture isolates and endoscopic samples (62.5% and 69.6%, respectively). However, many of these patients had evidence of mixed infection with cagA negative and cagA positive strais in cultures isolates and endoscopic samples (25% and 17.4%, respectively). Mixed infection was found to be due to genetically unrelated strains in two patients in whom genetic analysis was performed.
Conclusion. Mixed infection with differences in substrain pathogenic factors might occur in H. pylori infection and might contribute to differences in clinical outcome. 相似文献