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31.
32.
Kyriacou SK Mohamed A Miller K Neff S 《Biomechanics and modeling in mechanobiology》2002,1(2):151-164
Brain biomechanics has been investigated for more than 30 years. In particular, finite element analyses and other powerful
computational methods have long been used to provide quantitative results in the investigation of dynamic processes such as
head trauma. Nevertheless, the potential of these methods to simulate and predict the outcome of quasi-static processes such
as neurosurgical procedures and neuropathological processes has only recently been explored. Some inherent difficulties in
modeling brain tissues, which have impeded progress, are discussed in this work. The behavior of viscoelastic and poroelastic
constitutive models is compared in simple 1-D simulations using the ABAQUS finite element platform. In addition, the behaviors
of quasi-static brain constitutive models that have recently been proposed are compared. We conclude that a compressible viscoelastic
solid model may be the most appropriate for modeling neurosurgical procedures.
Received: 19 March 2002 / Accepted: 6 June 2002
Work is supported by a generous grant from the Whitaker Foundation. We would like to also thank Dr. Christos Davatzikos (Johns
Hopkins School of Medicine, Baltimore, Maryland) for his help. 相似文献
33.
In contrast to the beta-linked GlcNAc, the alpha-linked GlcNAc has not been commonly found in glycoconjugates. We have recently revealed the presence of an unusual endo-beta-galactosidase (Endo-beta-Gal(GnGa)) in Clostridium perfringens capable of releasing GlcNAcalpha1-->4Gal from glycans expressed in the gastric mucous cell-type mucin [Ashida, H., Anderson, K., Nakayama, J., Maskos, K., Chou, C.-W., Cole, R. B., Li, S.-C., and Li, Y.-T. (2001) J. Biol. Chem. 276, 28226-28232]. To characterize Endo-beta-Gal(GnGa), we have cloned its gene, gngC, from the genomic DNA library prepared from C. perfringens ATCC10543. The gene encodes 420 amino acid residues including a 17-residue signal peptide at the N-terminus. Using pUC18, we were able to prepare 25 mg of the fully active and pure recombinant Endo-beta-Gal(GnGa) from 1 L of Escherichia coli DH5alpha culture, which was 170 times higher than that produced by the original clostridial strain. Endo-beta-Gal(GnGa) shares a low but significant sequence similarity with two other endo-beta-galactosidases (16-21% amino acid identity). It also shows some similarity with bacterial 1,3-1,4-beta-glucan 4-glucanohydrolases of the glycoside hydrolase family 16. Endo-beta-Gal(GnGa) was found to contain the EXDX(X)E sequence (Glu-168 to Glu-173), that has been identified as the catalytic motif of families 16 and 7 retaining glycoside hydrolases. We have used site-directed mutagenesis to show that Glu-168 and Glu-173 were essential for the Endo-beta-Gal(GnGa) activity. By NMR spectroscopy, Endo-beta-Gal(GnGa) was found to act as a retaining enzyme. 相似文献
34.
Circumscription of the Malvales and relationships to other Rosidae: evidence from rbcL sequence data
Alverson W Karol K Baum D Chase M Swensen S McCourt R Sytsma K 《American journal of botany》1998,85(6):876-887
The order Malvales remains poorly circumscribed, despite its seemingly indisputable core constituents: Bombacaceae, Malvaceae, Sterculiaceae, and Tiliaceae. We conducted a two-step parsimony analysis on 125 rbcL sequences to clarify the composition of Malvales, to determine the relationships of some controversial families, and to identify the placement of the Malvales within Rosidae. We sampled taxa that have been previously suggested to be within, or close to, Malvales (83 sequences), plus additional rosids (26 sequences) and nonrosid eudicots (16 sequences) to provide a broader framework for the analysis. The resulting trees strongly support the monophyly of the core malvalean families, listed above. In addition, these data serve to identify a broader group of taxa that are closely associated with the core families. This expanded malvalean clade is composed of four major subclades: (1) the core families (Bombacaceae, Malvaceae, Sterculiaceae, Tiliaceae); (2) Bixaceae, Cochlospermaceae, and Sphaerosepalaceae (Rhopalocarpaceae); (3) Thymelaeaceae sensu lato (s.l.); and (4) Cistaceae, Dipterocarpaceae s.l., Sarcolaenaceae (Chlaenaceae), and Muntingia. In addition, Neurada (Neuradaceae or Rosaceae) falls in the expanded malvalean clade but not clearly within any of the four major subclades. This expanded malvalean clade is sister to either the expanded capparalean clade of Rodman et al. or the sapindalean clade of Gadek et al. Members of Elaeocarpaceae, hypothesized by most authors as a sister group to the four core malvalean families, are shown to not fall close to these taxa. Also excluded as members of, or sister groups to, the expanded malvalean clade were the families Aextoxicaceae, Barbeyaceae, Cannabinaceae, Cecropiaceae, Dichapetalaceae, Elaeagnaceae, Euphorbiaceae s.l., Huaceae, Lecythidaceae, Moraceae s.l., Pandaceae, Plagiopteraceae, Rhamnaceae, Scytopetalaceae, Ulmaceae, and Urticaceae. 相似文献
35.
Molecular Mechanism of Heat Shock-Provoked Disassembly of the Coliphage λ Replication Complex
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Alicja Wgrzyn Anna Herman-Antosiewicz Karol Taylor Grzegorz Wgrzyn 《Journal of bacteriology》1998,180(9):2475-2483
We have found previously that, in contrast to the free O initiator protein of λ phage or plasmid rapidly degraded by the Escherichia coli ClpP/ClpX protease, the λO present in the replication complex (RC) is protected from proteolysis. However, in cells growing in a complete medium, a temperature shift from 30 to 43°C resulted in the decay of the λO fraction, which indicated disassembly of RC. This process occurred due to heat shock induction of the groE operon, coding for molecular chaperones of the Hsp60 system. Here we demonstrate that an increase in the cellular concentration of GroEL and GroES proteins is not in itself sufficient to cause RC disassembly. Another requirement is a DNA gyrase-mediated negative resupercoiling of λ plasmid DNA, which counteracts DNA relaxation and starts to dominate 10 min after the temperature upshift. We presume that RC dissociates from λ DNA during the negative resupercoiling, becoming susceptible to the subsequent action of GroEL/S and ClpP/ClpX proteins. In contrast to λcro+, in λcro− plasmid-harboring cells, the RC reveals heat shock resistance. After temperature upshift of the λcrots plasmid-harboring cells, a Cro repressor-independent control of λ DNA replication and heat shock resistance of RC are established before the period of DNA gyrase-mediated negative supercoiling. We suggest that the tight binding of RC to λ DNA is due to interaction of RC with other DNA-bound proteins, and is related to the molecular basis of the λcro− plasmid replication control. 相似文献
36.
Oskar Wasielewski Tatiana Wojciechowicz Karol Giejdasz Natraj Krishnan 《Insect Science》2015,22(4):512-520
The effects of enhanced UV‐B radiation on the oogenesis and morpho‐anatomical characteristics of the European solitary red mason bee Osmia bicornis L. (Hymenoptera: Megachilidae) were tested under laboratory conditions. Cocooned females in the pupal stage were exposed directly to different doses (0, 9.24, 12.32, and 24.64 kJ/m2/d) of artificial UV‐B. Our experiments revealed that enhanced UV‐B radiation can reduce body mass and fat body content, cause deformities and increase mortality. Following UV exposure at all 3 different doses, the body mass of bees was all significantly reduced compared to the control, with the highest UV dose causing the largest reduction. Similarly, following UV‐B radiation, in treated groups the fat body index decreased and the fat body index was the lowest in the group receiving the highest dose of UV radiation. Mortality and morphological deformities, between untreated and exposed females varied considerably and increased with the dose of UV‐B radiation. Morphological deformities were mainly manifested in the wings and mouthparts, and occurred more frequently with an increased dose of UV. Cell death was quantified by the Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay (DNA fragmentation) during early stages of oogenesis of O. bicornis females. The bees, after UV‐B exposure exhibited more germarium cells with fragmented DNA. The TUNEL test indicated that in germarium, low doses of UV‐B poorly induced the cell death during early development. However, exposure to moderate UV‐B dose increased programmed cell death. In females treated with the highest dose of UV‐B the vast majority of germarium cells were TUNEL‐positive. 相似文献
37.
Protein quality control (proteostasis) depends on constant protein degradation and resynthesis, and is essential for proper homeostasis in systems from single cells to whole organisms. Cells possess several mechanisms and processes to maintain proteostasis. At one end of the spectrum, the heat shock proteins modulate protein folding and repair. At the other end, the proteasome and autophagy as well as other lysosome-dependent systems, function in the degradation of dysfunctional proteins. In this review, we examine how these systems interact to maintain proteostasis. Both the direct cellular data on heat shock control over autophagy and the time course of exercise-associated changes in humans support the model that heat shock response and autophagy are tightly linked. Studying the links between exercise stress and molecular control of proteostasis provides evidence that the heat shock response and autophagy coordinate and undergo sequential activation and downregulation, and that this is essential for proper proteostasis in eukaryotic systems. 相似文献
38.
The aim of the study was to verify botanical and ecological traits of river typology based on macrophytes. We compared diversities of macrophyte communities in different river types and their relationship to water quality. The 240 surveyed rivers were situated in the central-west of Poland in a lowland area. Species compositional similarities were analysed using the Jaccard index. The macrophyte matrix was classified into four groups: Large rivers (LR), Sandy rivers (SaR), Stony rivers (StR) and Organic rivers (OR). The highest level of homogeneity was found for LR, followed by OR, StR and SaR. The greatest differences in species composition were found between LR and StR. Variabilities of indices (species richness, Shannon, Simpson and Pielou indices, and total cover) confirmed the specific diversity patterns in the four types of rivers. All metrics based on relative abundance were strongly correlated with each other, and they were never correlated with water quality. The total covers of LR and OR as well as species richness of LR show some correlation with water quality. The total cover was correlated with water quality in OR and LR. The communities with the highest species richness were related with OR. 相似文献
39.
Bertova A Cacanyiova S Kristek F Krizanova O Ondrias K Tomaskova Z 《General physiology and biophysics》2010,29(4):402-410
As a part of the nitroso signalling pathway, nitroso-compounds serve as stores and carriers of NO; as part of the sulphide signalling pathway, bound sulfane-sulphur compounds serve as stores and carriers of H2S. Here we hypothesise a coupled sulphide-nitroso signalling pathway, in which H2S plays a main role. H2S releases NO from the endogenous S-nitroso-compounds nitroso-cysteine, nitroso-acetylcysteine and nitroso-albumin. Relaxation of noradrenaline-precontracted aortic rings by H2S is also enhanced in the presence of nitroso-albumin, which may implicate the involvement of the nitroso signalling pathway. Pretreatment of albumin, cysteine, N-acetylcysteine and lipids with H2S results in binding of sulphur to these compounds creating thus new-modified sulphur compounds that release NO from nitroso-compounds directly and/or through released H2S, which suggests sulphide-nitroso signalling pathway participation. This hypothesis is supported by the observation that the pretreatment of noradrenaline-precontracted aortic rings with H2S significantly enhanced relaxation induced by nitroso-glutathione in the absence of H2S. We assume that the NO release from nitroso-compounds directly by H2S or indirectly by the H2S-induced sulphur-bound compounds represents coupled sulphide-nitroso signalling, which may explain some of the numerous biological effects of H2S that are shared with NO. 相似文献
40.
Karol Marhold Hiroshi Kudoh Jae-Hong Pak Kuniaki Watanabe Stanislav ?paniel Judita Lihová 《Annals of botany》2010,105(2):249-264