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排序方式: 共有360条查询结果,搜索用时 15 毫秒
51.
Klara J Belzar Aiwu Zhou Robin W Carrell Peter G W Gettins James A Huntington 《The Journal of biological chemistry》2002,277(10):8551-8558
Antithrombin requires allosteric activation by heparin for efficient inhibition of its target protease, factor Xa. A pentasaccharide sequence found in heparin activates antithrombin by inducing conformational changes that affect the reactive center of the inhibitor resulting in optimal recognition by factor Xa. The mechanism of transmission of the activating conformational change from the heparin-binding region to the reactive center loop remains unresolved. To investigate the role of helix D elongation in the allosteric activation of antithrombin, we substituted a proline residue for Lys(133). Heparin binding affinity was reduced by 25-fold for the proline variant compared with the control, and a significant decrease in the associated intrinsic fluorescence enhancement was also observed. Rapid kinetic studies revealed that the main reason for the reduced affinity for heparin was an increase in the rate of the reverse conformational change step. The pentasaccharide-accelerated rate of factor Xa inhibition for the proline variant was 10-fold lower than control, demonstrating that the proline variant cannot be fully activated toward factor Xa. We conclude that helix D elongation is critical for the full conversion of antithrombin to its high affinity, activated state, and we propose a mechanism to explain how helix D elongation is coupled to allosteric activation. 相似文献
52.
Histone variant macroH2A contains
two distinct macrochromatin domains capable of directing macroH2A
to the inactive X chromosome 总被引:3,自引:0,他引:3
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Brian P. Chadwick Cory
M. Valley Huntington
F. Willard 《Nucleic acids research》2001,29(13):2699-2705
Chromatin on the inactive X chromosome (Xi) of female mammals is enriched for the histone variant macroH2A that can be detected at interphase as a distinct nuclear structure referred to as a macro chromatin body (MCB). Green fluorescent protein-tagged and Myc epitope-tagged macroH2A readily form an MCB in the nuclei of transfected female, but not male, cells. Using targeted disruptions, we have identified two macrochromatin domains within macroH2A that are independently capable of MCB formation and association with the Xi. Complete removal of the non-histone C-terminal tail does not reduce the efficiency of association of the variant histone domain of macroH2A with the Xi, indicating that the histone portion alone can target the Xi. The non-histone domain by itself is incapable of MCB formation. However, when directed to the nucleosome by fusion to core histone H2A or H2B, the non-histone tail forms an MCB that appears identical to that of the endogenous protein. Mutagenesis of the non-histone portion of macroH2A localized the region required for MCB formation and targeting to the Xi to an ~190 amino acid region. 相似文献
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55.
D. J. Wolff Karen M. Gustashaw Vickie Zurcher Lara Ko Wendy White Lester Weiss Daniel L. Van Dyke Stuart Schwartz Huntington F. Willard 《Human genetics》1997,100(2):256-262
High resolution cytogenetics, microsatellite marker analyses, and fluorescence in situ hybridization were used to define
Xq deletions encompassing the fragile X gene, FMR1, detected in individuals from two unrelated families. In Family 1, a 19-year-old
male had facial features consistent with fragile X syndrome; however, his profound mental and growth retardation, small testes,
and lover limb skeletal defects and contractures demonstrated a more severe phenotype, suggestive of a contiguous gene syndrome.
A cytogenetic deletion including Xq26.3–q27.3 was observed in the proband, his phenotypically normal mother, and his learning-disabled
non-dysmorphic sister. Methylation analyses at the FMR1 and androgen receptor loci indicated that the deleted X was inactive
in > 95% of his mother’s white blood cells and 80–85% of the sister’s leukocytes. The proximal breakpoint for the deletion
was approximately 10 Mb centromeric to FMR1, and the distal breakpoint mapped 1 Mb distal to FMR1. This deletion, encompassing
∼13 Mb of DNA, is the largest deletion including FMR1 reported to date. In the second family, a slightly smaller deletion
was detected. A female with moderate to severe mental retardation, seizures, and hypothyroidism, had a de novo cytogenetic
deletion extending from Xq26.3 to q27.3, which removed ∼12 Mb of DNA around the FMR1 gene. Cytogenetic and molecular data
revealed that ∼50% of her white blood cells contained an active deleted X. These findings indicate that males with deletions
including Xq26.3–q27.3 may exhibit a more severe phenotype than typical fragile X males, and females with similar deletions
may have an abnormal phenotype if the deleted X remains active in a significant proportion of the cells. Thus, important genes
for intellectual and neurological development, in addition to FMR1, may reside in Xq26.3–q27.3. One candidate gene in this
region, SOX3, is thought to be involved in neuronal development and its loss may partly explain the more severe phenotypes
of our patients.
Received: 19 December 1996 / Accepted: 13 March 1997 相似文献
56.
Jung JA Jhang E. John Staba Jung Yun Kim 《In vitro cellular & developmental biology. Plant》1974,9(4):253-259
Summary Roots, stems, or leaves of American (Panax quinquefolium) and Korean (Panax ginsing) ginseng were grown as callus or supension tissue cultures. Tissue cultures ofP. ginseng would occasionally form plantlets. The fundamental chemical composition, inorganic analysis, and saponin (panaquilin) content
of American and Korean ginseng plants and tissue cultures were determined. The crude saponin content is very similar to, but
approximately one-half (1.3%, fresh weight) of that present in ginseng roots. Two-dimensional thin layer chromatographic analysis
revealed minor differences in the panaquilins present in American and Korean ginseng tissue cultures. The sapogenin, panaxadiol,
was isolated from Korean ginseng callus. 相似文献
57.
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59.
ELECTRON MICROSCOPE STUDIES OF CRYSTAL-COLLAGEN RELATIONSHIPS IN BONE : IV. THE OCCURRENCE OF CRYSTALS WITHIN COLLAGEN FIBRILS 总被引:4,自引:2,他引:2
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Crystals are seen occasionally within the diameter of transversely sectioned collagen fibrils near the calcification front of newly formed bone. 相似文献
60.
JA Nboyine S Boyer D Saville MJ Smith SD Wratten 《New Zealand journal of zoology.》2016,43(4):336-350
The endemic New Zealand ground wētā (Hemiandrus sp. ‘promontorius’) has a Naturally Uncommon conservation status. This is because of the paucity of information on its density and distribution. Here, the biology, density and distribution of a population of this wētā found in and around vineyards in the Awatere Valley, Marlborough was studied. Wētā density was assessed in vineyards, paddocks and shrublands in this valley. Soil moisture, penetration resistance, pH and organic matter were recorded at locations with and without wētā. Wētā density in vineyards was significantly higher than in either paddocks or shrub habitats. In vineyards, the density of this insect was significantly higher under-vines than in the inter-rows. Higher numbers of this wētā were found in moist soils that required lower force to burrow. Females laid an average of 55 eggs between March and April, which hatched in September. These findings highlight the intersection between agriculture and conservation. 相似文献