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991.
浒苔多糖剂量150mg/kg可使高胆固醇血症小鼠血清胆固醇下降22%,剂量168mg/kg可使高脂血症大鼠TCH和TG分别降低58%和61%,HDL升高27%,剂量250mg/kg可分别提高血清、脑和肝SOD活力33%、118%和224%,剂量168mg/kg对高血脂大鼠血清和心脏LPO含量降低35%和46%。 相似文献
992.
Construction of a novel bifunctional biogenic amine receptor by two point mutations of the H2-histamine receptor.
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J. DelValle I. Gantz L. Wang Y. J. Guo G. Munzert T. Tashiro Y. Konda T. Yamada 《Molecular medicine (Cambridge, Mass.)》1995,1(3):280-286
BACKGROUND: H2-histamine receptors mediate a wide range of physiological functions extending from stimulation of gastric acid secretion to induction of human promyelocyte differentiation. We have previously cloned the H2-histamine receptor gene and noted that only three amino acids on the receptor were sufficient to define its specificity and selectivity. Despite only modest overall amino acid homology (34% amino acid identity and 57.5% similarity) between the H2-histamine receptor and the receptor for another monoamine, the beta 2-adrenergic receptor, there is remarkable similarity at their critical ligand binding sites. We hypothesized that, if the specificity and selectivity of both receptors are invested in just three amino acids, it should be possible to convert one of the receptors into one that recognizes the ligand of the other by simple mutations at only one or two sites. MATERIAL AND METHODS: We explored the effect of two single mutations in the fifth transmembrane domain of the H2-histamine receptor, which encompasses the sites that determine H2 selectivity. The canine H2 receptor gene was mutated at Asp186 and Gly187 (Asp186 to Ala186 and Gly187 to Ser187) by oligonuceotide directed mutagenesis. The coding region of both the wild-type and mutated H2 receptors was subcloned into the eukaryotic expression vector, CMVneo, and stably transfected into Hepa cells and L cells. The biological activity of histamine and epinephrine on the expressed receptor was examined by measurement of cellular cAMP production and inositol trisphosphate formation. RESULTS: Hepa cells transfected with the Ala186-Ser187 mutant H2 receptor demonstrated a biphasic rise in cAMP in response to epinephrine with an early phase (ED50 approximately 10(-11) M) that could be inhibited by both propranolol and cimetidine. Epinephrine also induced IP3 generation in the same cells, a biological response that is characteristic of activation of the wild-type H2 but not of the beta-adrenergic receptor. L cells transfected with the Ala186-Ser187 mutant H2 receptor also responded to epinephrine in a cimetidine and propranolol inhibitable manner. CONCLUSIONS: We converted the H2-histamine receptor into a bifunctional one that has characteristics of both histamine and adrenergic receptors by two simple mutations. These results support the hypothesis that ligand specificity is determined by only a few key points on a receptor regardless of the structure of the remainder of the molecule. Our studies have important implications on the design of pharmacological agents targeted for action at physiological receptors. 相似文献
993.
Kan Wang Paul Drayton Bronwyn Frame Jim Dunwell John Thompson 《In vitro cellular & developmental biology. Plant》1995,31(2):101-104
A number of different methods, involving direct DNA delivery are now available for plant transformation. Here we review the most recently developed technique which involves the mixing of silicon carbide whiskers with plant cells and plasmid DNA. Fertile transgenic plants have now been produced using whisker-mediated transformation, and this method can now be considered as a simple, inexpensive alternative for plant transformation. A brief review on transformation of animal cells andChlamydomonas using whiskers technology is also included. 相似文献
994.
An RNA pseudoknot is an essential structural element of the internal ribosome entry site located within the hepatitis C virus 5' noncoding region. 总被引:8,自引:2,他引:6
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Translation of the human hepatitis C virus (HCV) RNA genome occurs by a mechanism known as "internal ribosome entry." This unusual strategy of translation is employed by naturally uncapped picornaviral genomic RNAs and several cellular mRNAs. A common feature of these RNAs is a relatively long 5' noncoding region (NCR) that folds into a complex secondary structure harboring an internal ribosome entry site (IRES). Evidence derived from the use of dicistronic expression systems, combined with an extensive mutational analysis, demonstrated the presence of an IRES within the HCV 5'NCR. The results of our continued mutational analysis to map the critical structural elements of the HCV IRES has led to the identification of a pseudoknot structure upstream of the initiator AUG. The evidence presented in this study is based upon the mutational analysis of the putative pseudoknot structure. This is further substantiated by biochemical and enzymatic probing of the wild-type and mutant 5'NCR. Further, the thermodynamic calculations, based upon a modified RNAKNOT program, are consistent with the presence of a pseudoknot structure located upstream of the initiator AUG. Maintenance of this structural element is critical for internal initiation of translation. The pseudoknot structure in the 5'NCR represents a highly conserved feature of all HCV subtypes and members of the pestivirus family, including hog cholera virus and bovine viral diarrhea virus. 相似文献
995.
家鸡和原鸡的线粒体DNA多态性比较 总被引:17,自引:0,他引:17
本文运用11种限制性内切酶分析了家鸡(茶花鸡、尼西鸡、大理漾濞黄鸡)和原鸡共10只个体的线粒体DNA限制性片段长度多态性(RFLP),平均每个个检测到的片段为40条左右。但仅发现3种变异的限制性片制性格局,即StuI-B,Eca-I-b和RI-B.其中StuI-B和ScaI-B为首次报道,而且均为原鸡所物有,EcoRI-B则为大理漾濞黄鸡所特有。茶花鸡和尼西鸡拥有完全相同的限制性格局。经过计算,原 相似文献
996.
997.
The degradation of cytoplasmic antigens to peptides presented by class I MHC molecules is thought to be mediated by the ubiquitin/proteasome pathway. Support for this view came from our observation that the subunit composition of proteasomes can be changed by interferon-gamma (IFN-gamma) treatment. Thereby two subunits, LMP2 and LMP7, which are encoded in the MHC class II region, are incorporated into the proteasomal complex, whereas other subunits disappear. In the experiments reported in this communication we studied the subunit changes occurring in cell lines where the expression of LMP2 or LMP7 can be regulated individually either by IFN-gamma induction or by applying a new system to control the expression of transfected LMPs. In both situations LMP2 induction leads exclusively to the disappearance of housekeeping subunit 2, whereas LMP7 affects only subunit 10. Subunit 2 was found to be 76% homologous to LMP2. Since incorporation of LMP2 into the proteasomal complex prevents processing of the subunit 2 precursor, we conclude that LMP2 displaces subunit 2 during assembly. Subunit displacement is most likely a general mechanism to modulate the catalytic activity of the proteasomal complex without changing its structure. Furthermore, the controlled incorporation of transfected subunits into the complex offers a new approach to study proteasome function in vivo. 相似文献
998.
Type 1 protein phosphatase acts in opposition to IpL1 protein kinase in regulating yeast chromosome segregation. 总被引:19,自引:6,他引:13
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The IPL1 gene is required for high-fidelity chromosome segregation in the budding yeast Saccharomyces cerevisiae. Conditional ipl1ts mutants missegregate chromosomes severely at 37 degrees C. Here, we report that IPL1 encodes an essential putative protein kinase whose function is required during the later part of each cell cycle. At 26 degrees C, the permissive growth temperature, ipl1 mutant cells are defective in the recovery from a transient G2/M-phase arrest caused by the antimicrotubule drug nocodazole. In an effort to identify additional gene products that participate with the Ipl1 protein kinase in regulating chromosome segregation in yeast, a truncated version of the previously identified DIS2S1/GLC7 gene was isolated as a dosage-dependent suppressor of ipl1ts mutations. DIS2S1/GLC7 is predicted to encode a catalytic subunit (PP1C) of type 1 protein phosphatase. Overexpression of the full-length DIS2S1/GLC7 gene results in chromosome missegregation in wild-type cells and exacerbates the mutant phenotype in ipl1 cells. In addition, the glc7-1 mutation can partially suppress the ipl1-1 mutation. These results suggest that type 1 protein phosphatase acts in opposition to the Ipl1 protein kinase in vivo to ensure the high fidelity of chromosome segregation. 相似文献
999.
1000.
Uri S. Ladror Gary T. Wang William L. Klein Thomas F. Holzman Grant A. Krafft 《Journal of Protein Chemistry》1994,13(4):357-366
Fluorogenic peptide substrates designed to encompass the reported-secretory and amyloidogenic cleavage sites of the amyloid- precursor protein (PP) were used to analyze proteinase activities in brain extracts from control patients and those with Alzheimer's disease (AD). Activity against the secretory substrate atpH 7.5 in control and AD brains produced a major endopeptidase cleavage at the Lys687-Leu688 bond (PP770 numbering), consistent with thePP secretase cleavage. Activity in control brains against the amyloidogenic substrate atpH 7.5 produced one cleavage at the Ala673-Glu674 bond, two residues C-terminal to the amyloidogenic Met-Asp site. However, in three of four AD brains, the major cleavage was at the Asp-Ala bond, one residue from the amyloidogenic site. Both endopeptidase and carboxypeptidase activities in AD brains were lower than in control brains. Proteinase activities against the secretory substrate had a major optimum atpH 3.0–4.0 and another atpH 6.0–7.5. Proteinase activities against the amyloidogenic substrate had a major optimum at or belowpH 3.0 and another atpH 6.0. Using both substrates, activities at lowpH were higher in AD brains than in controls, while atpH above 6.5, activities in control brains were higher than in AD. These results indicate that the levels of proteolytic enzymes in AD brains are altered relative to controls.Abbreviations A
Amyloid-
- ACN
acetonitrile
- AD
Alzheimer's disease
- PP
amyloid- precursor protein
- DABCYL
4-(4-dimethylaminophenylazo)-benzoic acid
- EDANS
5-{(2-aminoethyl)amino}napthalene-1-sulfonic acid
- MES
morpholinoethane sulfonic acid
- MOPS
morpholino-propane sulfonic acid
- RP-HPLC
reverse-phase high-performance liquid chromatography
- SDS-PAGE
sodium do-decyl sulfate-polyacrylamide gel electrophoresis
- TFA
tri-fluoroacetic acid
- Tris
tris(hydroxyethyl)aminomethane 相似文献