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本文利用激光散斑屈光测试系统详细探讨了夜近视(night myopia)的产生机制。夜近视在环境亮度降低到产生暗视觉时出现,并随亮度继续降低而增大,平均值为1.35D。实验证明眼睛球差和色差不是造成夜近视的主要因素。夜近视数值在暗适应过程中呈增大的趋势。在暗视觉时,由于视野中缺少适宜的刺激,眼睛处于暗焦(dark focus)休止状态,这是造成夜近视的主要原因。 相似文献
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Biochemical and genetic characterization of three hamster cell mutants resistant to diphtheria toxin 总被引:2,自引:0,他引:2
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RK Draper D Chin D Eurey-Owens IE Scheffler MI Simon 《The Journal of cell biology》1979,83(1):116-125
We describe here three different hamster cell mutants which are resistant to diphtheria toxin and which provide models for investigating some of the functions required by the toxin inactivates elongation factor 2 (EF-2). Cell-free extracts from mutants Dtx(r)-3 was codominant. The evidence suggests that the codominant phenotype is the result of a mutation in a gene coding for EF-2. The recessive phenotype might arise by alteration of an enzyme which modifies the structure of EF-2 so that it becomes a substrate for reaction with the toxin. Another mutant, Dtx(r)-2, contained EF-2 that was sensitive to the toxin and this phenotype was recessive. Pseudomonas aeruginosa exotoxin is known to inactivate EF-2 as does diphtheria toxin and we tested the mutants for cross-resistance to pseudomonas exotoxin. Dtx(r)-1 and Dtx(r)-3 were cross-resistant while Dtx(r)-2 was not. It is known that diphtheria toxin does not penetrate to the cytoplasm of mouse cells and that these cell have a naturally occurring phenotype of diphtheria toxin resistance. We fused each of the mutants with mouse 3T3 cells and measured the resistance. We fused each of the mutants with mouse 3T3 cells and measured the resistance of the hybrid cells to diphtheria toxin. Intraspecies hybrids containing the genome of mutants Dtx(r)-1 and Dtx(r)-3 had some resistance while those formed with Dtx(r)-2 were as sensitive as hybrids derived from fusions between wild-type hamster cells and mouse 3T3 cells. 相似文献
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IE Hughes 《BioEssays : news and reviews in molecular, cellular and developmental biology》1999,21(11):980-981
Instant Pharmacology (1999). Saeb-Parsy K, Assomull RG, Kahn FZ, Saeb-Parsy K, and Kelly E. John Wiley and Sons 349 pp. £19.99 pbk; ISBN 0471976393 © 1999 John Wiley & Sons, Inc. 相似文献
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本文用脑室灌注和Fura2测定细胞内游离钙技术观察了地塞米松(dexamethasone,DEX)对家兔乙二醇双(2氨基乙醚)四乙酸性发热效应和下丘脑细胞内游离钙浓度([Ca2+]i)的影响,借此深入探讨地塞米松解热作用的中枢机制。结果发现:脑室灌注乙二醇双(2氨基乙醚)四乙酸(06nmol)引起家兔结肠温度明显升高,静脉注射地塞米松(5mg/kg)显著抑制家兔乙二醇双(2氨基乙醚)四乙酸性发热,地塞米松(60~120μmol/L)并不影响下丘脑细胞内[Ca2+]i,而事先脑室灌注抑制基因转录的放线菌素D(3nmol)则完全取消了地塞米松对乙二醇双(2氨基乙醚)四乙酸性发热的解热作用。这些结果提示:地塞米松显著抑制家兔乙二醇双(2氨基乙醚)四乙酸性发热,其机制与地塞米松激活脑内某些基因的表达有关,而与下丘脑神经细胞跨膜钙离子流无关。 相似文献
5.
Pristiazhniuk IE Temirova SA Menzorov AG Kruglova AA Matveeva NM Serov OL 《Ontogenez》2005,36(2):151-158
Chromosome segregation of the parental chromosomes was studied in 20 interspecific hybrid clones obtained by fusion of Mus musculus embryonic stem cells with Mus caroli splenocytes. FISH analysis with labeled species specific probes and microsatellite markers was used for identification of the parental chromosomes. Cytogenetic analysis has shown significant intra- and interclonal variability in chromosome numbers and ratios of the parental chromosomes in the hybrid cells: six clones contained all M. caroli chromosomes, nine clones showed moderate segregation of M. caroli chromosomes (from 1 to 7), and five clones showed extensive loss of M. caroli chromosomes (from 12 to complete loss of all M. caroli autosomes). Both methods demonstrated "cryptic" segregation of the somatic partner chromosomes. For instance, five clones with near-tetraploid chromosome sets contained only few M. caroli chromosomes (from 1 to 8). The data obtained suggest that the tetraploid chromosome set per se is not a sufficient criterion for conclusion on the absence of chromosome loss in the hybrid cells. Note that "cryptic" chromosome segregation occurred at a high frequency in the examined hybrid clones. Thus, "cryptic" segregation should be borne in mind for assessing pluripotency and genome reprogramming of embryonic stem hybrid cells. 相似文献
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The distribution of the Golgi enzyme beta1, 6-N-
acetylglucosaminyltransferase (core 2 GlcNAc-T for short) has been
investigated in several tissue and cell systems by combining the potentials
of a polyclonal antibody and a novel, sensitive fluorescent enzyme assay.
In normal rat tissues, levels of the protein were found to vary and as a
general trend did not correlate with enzyme activities. Additionally, we
observed tissue-specific core 2 GlcNAc-T forms of various size: 75 kDa
(liver), 70 kDa (spleen), 60 kDA (heart), and 50 kDa (heart and lung).
These forms might arise from differential protein modifications;
alternatively, the smaller form may be a product of proteolytic cleavage,
given the presence of a catalytically inactive 50 kDa species in rat serum.
Chinese hamster ovary (CHO), MDAY-D2, PSA- 5E, and PYS-2 cell lines
consistently displayed a 70 kDa enzyme. When induced to retrodifferentiate
in the presence of butyrate + cholera toxin, CHO cells exhibited a 21-fold
increase in enzyme activity, while protein levels remained constant. A
similar trend was observed in the embryonal endoderm cell lines PSA-5E and
PYS-2, where an approximately 100-fold difference in core 2 GlcNAc-T
activity was found notwithstanding unchanged amounts of the protein and
identical mRNA levels, as evidenced by RT-PCR. In contrast, levels of core
2 GlcNAc-T activity in MDAY-D2 cells correlated well with protein
expression. Taken together, these observations demonstrate that core 2
GlcNAc-T expression may be subjected to multiple mechanisms of regulation
and suggest that in at least some instances (i.e., PSA-5E and PYS-2 cells)
expression may be regulated exclusively via posttranslational mechanism(s)
of control.
相似文献
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基于PBL模式的生物化学教学探索 总被引:1,自引:1,他引:0
目的:评价PBL教学模式在生物化学中应用的教学效果,对生物化学理论教学的方式进行探讨。方法:用PBL模式进行教学,采用理论考试的形式对教学效果进行评价。结果:PBL教学组的学生在学习态度和积极性等方面好于传统教学组;在考试成绩方面PBL教学组病例分析考试成绩好于传统教学组,而基础知识考试成绩没有差别。结论:PBL模式能提高学生的分析问题和解决问题的综合应用能力,而基础知识的掌握程度与传统教学相比没有区别。 相似文献
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用 m RNA差异显示 PCR技术 ,从人 1 8周、2 2周胎儿脑和肝肾组织的 m RNA逆转录产物得到一些特异性显示的片段 .其中一个随机片段 GC1 0 2作为探针 ,从本实验室构建的 1 8周胎儿脑c DNA基因文库进行杂交筛选 ,得到一个阳性克隆λ gt1 0 /GC1 0 2 .该克隆内插入的 c DNA片段长2 .9kb,经过 DNA测序 ,显示具有一个开放阅读框架 ,编码 1 37个氨基酸的肽链 .用蛋白质结构的建模软件预测了该肽链的立体结构初步模型 . 相似文献
10.
Serov OL Matveeva NM Kizilova EA Kuznetsov SB Zhelezova AI Golubitsa AN Pristiazhniuk IE Puzakov MV 《Ontogenez》2003,34(3):216-227
In the hybrid cells obtained by fusion of embryonic stem cells with adult differentiated cells, homologous chromosomes are in two ontogenetic configurations: pluripotent and differentiated. In order to assess the role of cis- and trans-regulation in the maintenance of these states, we studied a set of clones of hybrid cells of the type embryonic stem cells-splenocytes and used two approaches: segregation of parental chromosomes and comparison of pluripotency of the past hybrid cells and embryonic stem cells. The segregation test showed that the hybrid cells lost only the homologs of the somatic partner and this process was sharply accelerated when the cells were cultivated in nonselective conditions, thus suggesting the full or partial preservation of the initial differences in the organization of parental homologs. The descendants of the former hybrid cells, which had the karyotype similar to that of embryonic stem cells, demonstrated the level of pluripotency, comparable with that of embryonic stem cells despite the long-term effect of trans-acting factors from the somatic partner in the genome of hybrid cells. The data obtained are interpreted in the framework of the concept of "chromosome memory", in the maintenance of which the key role is played by cis-regulatory factors. 相似文献
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