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91.
The gene (alyVI) encoding an alginate lyase of marine bacterium Vibrio sp. QY101, which was isolated from a decaying thallus of Laminaria, was cloned using a strategy of combined degenerate PCR and long range-inverse PCR (LR-IPCR), then sequenced and expressed in Escherichia coli. Gene alyVI was composed of a 1014 bp open reading frame (ORF) encoding 338 amino acid residues. The calculated molecular mass of alyVI product is 38.4 kDa, but a signal peptide is cleaved off, leaving a mature protein of 34 kDa. AlyVI was purified from culture supernatants to electrophoretic homogeneity using affinity chromatography. AlyVI was most active at pH 7.5 and 40 degrees C in the presence of 1 mM ZnCl2. A nine-amino-acid consensus region (YXRESLREM), which was only found in polyguluronate lyases, was also observed in the amino-terminal region of AlyVI. However, AlyVI could degrade both M block and G block. These results indicate that a novel alginate lyase-encoding gene has been cloned. 相似文献
92.
本文对高原冻伤中血液循环障碍作形态计量,旨在探讨血循环障碍在冻伤过程中的变化及高原冻伤发病机理中所起的作用。实验选用Wistar雄性大鼠40只,随机分为平原冻伤组、急性低氧冻伤组和低氧习服冻伤组。习服组动物于低压舱内模拟海拔6000m缺氧每日4h,连续两周。其余动物常规饲养。习服期满次日习服组与低氧组一同进入舱内模拟海拔6000m低氧4h,再行冷冻。冻后继续低氧4h。冻后48h取材。对各组动物冻后48h冻肢皮下血管的病变作图象分析。结果发现,平原组血管淤滞、血栓绝对数及其百分比均为最低,习服组最高,低氧组居中。但低氧组与平原组的血栓/淤滞百分比无明显差别。骨骼肌坏死的面积百分比习服组显著高于低氧组与平原组,而后两组间无差别。血栓/淤滞百分比与骨骼肌坏死面积百分比之间的有高度相关关系。冻融是直接引起血管内皮损伤的原发因素,局部血液循环障碍是造成严重的继发损伤的主要原因。 相似文献
93.
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95.
核糖核酸(RNA)与稀土铽离子在pH5.0~6.5条件下能形成具有较强荧光的络合物,其激发峰在288nm处,发射峰为494nm及545nm处.RNA在0.1~10mg/L范围内与其荧光强度呈线性关系,其检出限为6.0×10 ̄(-8)mol/L.腺苷酸,尿苷酸,胞苷酸对RNA的干扰比较小,因此可在其存在下选择性地测定RNA. 相似文献
96.
Cell signaling and heat shock protein expression 总被引:5,自引:0,他引:5
Exposure of cells and organs to heat shock is associated with numerous changes in various cellular metabolic parameters and overexpression of proteins collectively known as heat shock proteins (HSP). In this communication we review the cell-signaling events that are altered in response to heat shock as they relate to the subsequent induction of HSP 70 kd (HSP-70) expression. We also review the mechanisms by which HSP-70 is involved in conferring cytoprotective effects. The possibility of altering HSP expression through manipulations of the cell-signal process has clinical importance.The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the Department of the Army or Department of Defense. 相似文献
97.
Chou-Chik Ting Myrthel E. Hargrove Jie Wang Aneeta D. Patel 《Cellular immunology》1995,160(2):286-296
This study examined the role of protein tyrosine kinase (PTK) and protein kinase C (PKC) in the signal transduction pathways for lymphocyte activation through IL-2R to generate LAK cells and through TCR—CD3 to generate CD3-AK cells. Two PTK inhibitors [herbimycin A and genistein (PTK-I)] and two PKC inhibitors [calphositin C and staurosporine (PKC-I)] were used in the experiments. It was found that the primary activation pathway through IL-2R was PTK-dependent; that is, generation of both the IL-2-induced proliferative and the cytotoxic responses was completely abrogated by PTK-I and not by PKC-I. Quite different results were obtained with the αCD3-induced CD3-AK cell response. First, the αCD3-induced proliferation was only partially inhibited by PTK-I or PKC-I alone. Second, generation of CD3-AK cytotoxic response was primarily PKC-dependent; that is, only PKC-I induced significant inhibition. Genistein was found to reduce protein tyrosine phosphorylation in both LAK cells and CD3-AK cells, indicating that CD3-AK cells were also susceptible to PTK-I treatment. Further studies showed that PTK-I and not PKC-I suppressed perforin mRNA expression and N-2-benzyoxycarbonyl-l-lysine thiobeneylester esterase production in LAK cells, and the opposite was true for CD3-AK cells. These results indicate that different pathways were employed in lymphocyte activation through IL-2R and TCR—CD3. The former pathway is primarily PTK-dependent. Activation through TCR—CD3 is a more complex event. Induction of a proliferative response can employ either a PTK- or a PKC-dependent pathway, whereas induction of a cytotoxic response is primarily PKC-dependent. Furthermore, it appears that a PTK-independent pathway exists for the induction of a CD3-AK response and thus suggests that activation of the second messenger PKC may not necessarily be preceded by PTK activation. 相似文献
98.
The role of context on alpha-helix stabilization: host-guest analysis in a mixed background peptide model. 总被引:1,自引:1,他引:0
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J. Yang E. J. Spek Y. Gong H. Zhou N. R. Kallenbach 《Protein science : a publication of the Protein Society》1997,6(6):1264-1272
The helix content of a series of peptides containing single substitutions of the 20 natural amino acids in a new designed host sequence, succinyl-YSEEEEKAKKAXAEEAEKKKK-NH2, has been determined using CD spectroscopy. This host is related to one previously studied, in which triple amino acid substitutions were introduced into a background of Glu-Lys blocks completely lacking alanine. The resulting free energies show that only Ala and Glu- prove to be helix stabilizing, while all other side chains are neutral or destabilizing. This agrees with results from studies of alanine-rich peptide modela, but not the previous Glu-Lys block oligomers in which Leu and Met also stabilize helix. The helix propensity scale derived from the previous block oligomers correlated well with the frequencies of occurrence of different side chains in helical sequences of proteins, whereas the values from the present series do not. The role of context in determining scales of helix propensity values is discussed, and the ability of algorithms designed to predict helix structure from sequence is compared. 相似文献
99.
Incipient Speciation by Sexual Isolation in Drosophila Melanogaster: Extensive Genetic Divergence without Reinforcement
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The collection of Drosophila melanogaster from Zimbabwe and nearby regions (the Z-type) yield females who would not mate with the cosmopolitan D. melanogaster males (the M-type). To dissect the genetic basis of this sexual isolation, we constructed 16 whole-chromosome substitution lines between two standard Z-and M-lines. The results were as follows: (1) All substitution lines appear normal in viability and fertility in both sexes, indicating no strong postmating isolation. (2) The genes for the behaviors are mapped to all three major chromosomes with the same ranking and comparable magnitude of effects for both sexes: III > II >> X >/= 0 (III, II and X designate the effects of the three chromosomes). The results suggest less evolution on the X than on autosomes at loci of sexual behavior. (3) The genes for ``Z-maleness' are many and somewhat redundant. Whole-chromosome effects for Z-maleness appear nearly additive and show little dominance. (4) In contrast, ``Z-femaleness' has less redundancy as partial genotypes never exhibit full phenotypic effects. Epistatic interactions and incomplete dominance can sometimes be detected. (5) The extensive genetic divergence underlying sexual isolation has evolved in the absence of detectable reduction in hybrid fitnesses. Sexual selection has apparently been a driving force of multiple facets of speciation at the nascent stage without reinforcement. 相似文献
100.