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991.
报道了一个不需同位素和HPLC的α-1,6-岩藻糖转移酶(α1,6FuT,又称核心岩藻糖转移酶)的测定法,包括从正常人血浆提纯运铁蛋白,消化成带有天冬酰胺(Asn)的二天线N-糖链,去除外端唾液酸和半乳糖后,用生物素酰胺乙酰基团标记其Asn,并以此生物素衍生物标记的Asn-七糖的N-糖链为受体底物,GDP-L-岩藻糖为供体底物,用LCA柱吸附法分离岩藻糖化后的产物,再用HRp-Avidin交联物与柱上带有生物素的产物结合,此HRP-Avidin-生物素。岩藻糖化产物从柱上洗脱后测定HRP活力可代表α1,6FuT活力。此法在较宽的范围内,产物量与酶量和反应时间成正比.人肝细胞癌、亚硝胺诱发大鼠肝癌后期或用佛波酯(PMA)处理人肝癌细胞后,α1,6FuT增高,而用视黄酸或db-cAMP处理人肝癌细胞后,则该酶活力降低。 相似文献
992.
993.
994.
Douglas Laurents Jos Manuel Prez‐Caadillas Jorge Santoro Manuel Rico David Schell C. Nick Pace Marta Bruix 《Proteins》2001,44(3):200-211
We have used NMR methods to characterize the structure and dynamics of ribonuclease Sa in solution. The solution structure of RNase Sa was obtained using the distance constraints provided by 2,276 NOEs and the C6-C96 disulfide bond. The 40 resulting structures are well determined; their mean pairwise RMSD is 0.76 A (backbone) and 1.26 A (heavy atoms). The solution structures are similar to previously determined crystal structures, especially in the secondary structure, but exhibit new features: the loop composed of Pro 45 to Ser 48 adopts distinct conformations and the rings of tyrosines 51, 52, and 55 have reduced flipping rates. Amide protons with greatly reduced exchange rates are found predominantly in interior beta-strands and the alpha-helix, but also in the external 3/10 helix and edge beta-strand linked by the disulfide bond. Analysis of (15)N relaxation experiments (R1, R2, and NOE) at 600 MHz revealed five segments, consisting of residues 1-5, 28-31, 46-50, 60-65, 74-77, retaining flexibility in solution. The change in conformation entropy for RNase SA folding is smaller than previously believed, since the native protein is more flexible in solution than in a crystal. 相似文献
995.
Optimal harvesting of stochastically fluctuating populations 总被引:5,自引:0,他引:5
We obtain the optimal harvesting plan to maximize the expected discounted number of individuals harvested over an infinite future horizon, under
the most common (Verhulst-Pearl) logistic model for a stochastically fluctuating population. We also solve the problem for the standard variants of the model
where there are constraints on the admissible harvesting rates. We use stochastic calculus to derive the optimal population
threshold at which individuals are harvested as well as the overall value of the population in the sense of the model. We
show that except under extreme conditions, the population is never depleted in finite time, but remains in a stationary distribution which we find explicitly. Needless to say, our results
prove that any strategy which totally depletes the population is sub-optimal. These results are much more precise than those
previously obtained for this problem.
Received 24 June 1996; received in revised form 7 April 1997 相似文献
996.
本实验于1992年底开始,通过选种、选配,建立了一个11只雄猴,77只雌猴的恒河猴生产繁殖种群并对其繁殖性能进行了观察与研究。三年间,利用大笼群养的“后宫式”繁殖方法,母猴怀孕107例,流产11例,生产仔猴96只,离乳94只。平均妊娠率、产仔率、离乳率分别为51.44%、46.15%、97.92%。在“后宫式”群养方式繁殖成功后,我们又尝试了单笼饲养、定期交配的新的繁殖方法,当年投种9只母猴,怀孕7只,生产7只。怀孕率、生产率均为77.78%。在进行实验性繁殖的同时,对人工条件下饲养的恒河猴的部分生物学特性如妊娠期、月经周期、血液生理生化指标、生长特性等进行了观察、记录和统计。结果表明人工条件下饲养的恒河猴在每年11月至次年4月间交配,4月至9月分娩。恒河猴具有间情期,每年秋冬季发情,平均月经周期为28.31±2.82d(n=70)。平均怀孕期为163.46±11.87d(n=13)。本实验为人工繁殖恒河猴进而实现实验动物化积累了基础数据,为将来提供高等级的、遗传背景清楚的、高质量的实验猕猴奠定了工作基础。 相似文献
997.
Fumiko Nishikawa Eiji Kita Norio Matsui Shuzo Kashiba 《Microbiology and immunology》1994,38(3):201-207
The effector cells responsible for protection to Salmonella typhimurium in C3H/HeJ mice, conferred by L-form S. typhimurium, were determined by cell transfer test. Nonfractionated spleen cells from 6-week immune mice but not from 24-week immune animals transferred anti-S. typhimurium immunity. Treatment with anti-macrophage antiserum and complement most effectively abolished protective capacity in 6-week immune cells, while anti-T cell monoclonal antibody plus complement reduced it to a lesser extent. However, adoptive protection was achieved only by transfer of immune macrophages along with Lyt-2+ T cells selected from 6-week immune spleen cells. These Lyt-2+ T cells were cytotoxic to Kupffer cells from C3H/HeJ mice which had been infected 48 hr previously and from the mice which had been immunized 1 week previously, but not to the cells from 6-week immune mice and from normal animals. Moreover, protective capacity in immune macrophages seemed to be correlated to the degree of colonization by the L forms, and the inability to transfer immunity of 24-week immune spleen cells may be due to the decrease in the L form-colonization. These results suggest that cooperation between the L form-colonized macrophages and L form-induced cytotoxic Lyt-2+ T cells contributes to anti-S. typhimurium immunity, and might imply the immunological difference between the 6-week immune phagocytes and the cells at an early stage of infection or immunization. 相似文献
998.
α-苦瓜子蛋白晶体结构中的次级相互作用的研究──Ⅰ结构中氢键相互作用的分析 总被引:1,自引:1,他引:0
α-苦瓜子蛋白是一种单链核糖体失活蛋白,具有N-糖苷酶活性,2.0A分辨率的三维结构已经测定。α-苦瓜子蛋白中总共有353个氢键,其中主链原子间氢键165个,主链原子与侧链原子间氢键54个,侧链原子间氢键21个,蛋白分子中原子与溶水剂的氢键113个,主链C=O,主链NH及侧链分子结构中有95%的残基能生成氢键,Asp.Glu、Asn、Gln具有较强的生成多个氢键的能力,并对13个没有任何氢键的残基作了分析。An、Leu、Ile、GlU、Gln在α螺旋中出现税率较大,Val、Leu、Tyr、Ile、Thr在β结构中占了一半以上,Arg容易形成远程的氢键,而Ser、Thr则容易形成近程氢键。某些氢键,特别是保守残基间的氢键,对形成蛋白分子局部特征构象和活性部位的特征构象有影响,α-苦瓜子蛋白的特定折叠方式对其与溶剂水分子成氢键有影响。 相似文献
999.
以伤寒─鼠伤寒双价重组株Vi4072的3×108CFU一次口服感染BALB/C小鼠,4天后即可从小鼠的集合淋巴结、肝、脾中分离到该菌,49天后该菌始被小鼠机体彻底清除。血清和小肠匀浆液中Vi抗体检测结果证明Vi4072菌株有刺激特异性免疫应答的功能。血清、小肠匀浆液中Vi抗体明显升高。 相似文献
1000.
N. Galarce B. Escobar V. Rojas C. Navarro G. Turra J. Robeson 《Biocontrol Science and Technology》2016,26(4):462-475
Salmonella enterica serotype Enteritidis (SE) is a major cause of food-borne disease outbreaks worldwide. We evaluated the effectiveness of five lytic bacteriophages applied as a cocktail to reduce the counts of SE in two types of processed meat products: cooked (turkey ham (TB) and chicken sausage (CS)) and cured sausage (Italian salami (IS) and barbecue sausage (BS)). Groups of 25 samples each were contaminated with SE, treated with a phage cocktail using a multiplicity of infection of 105 and then incubated for ten days at 18°C and 4°C. A significant reduction in bacteria was obtained on days 3, 6 and 10 in all matrices incubated at 18°C (from 0.48 to 2.12?log Colony Forming Units (CFU)?g?1) and at 4°C (from 0.23 to 2.06?log CFU?g?1), with the exception of BS at day 3 at 4°C, and IS at both incubation temperatures throughout the trial. The viral titre remained stable in all matrices analysed except in BS. These results show the effectiveness of this bacteriophage cocktail against S. enterica serovar Enteritidis in some processed meat products such as CS, BS and TB. 相似文献