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941.
Miga MI Paulsen KD Hoopes PJ Kennedy FE Hartov A Roberts DW 《Journal of biomechanical engineering》2000,122(4):354-363
Current brain deformation models have predominantly reflected solid constitutive relationships generated from empirical ex vivo data and have largely overlooked interstitial hydrodynamic effects. In the context of a technique to update images intraoperatively for image-guided neuronavigation, we have developed and quantified the deformation characteristics of a three-dimensional porous media finite element model of brain deformation in vivo. Results have demonstrated at least 75-85 percent predictive capability, but have also indicated that interstitial hydrodynamics are important. In this paper we investigate interstitial pressure transient behavior in brain tissue when subjected to an acute surgical load consistent with neurosurgical events. Data are presented from three in vivo porcine experiments where subsurface tissue deformation and interhemispheric pressure gradients were measured under conditions of an applied mechanical deformation and then compared to calculations with our three-dimensional brain model. Results demonstrate that porous-media consolidation captures the hydraulic behavior of brain tissue subjected to comparable surgical loads and that the experimental protocol causes minimal trauma to porcine brain tissue. Working values for hydraulic conductivity of white and gray matter are also reported and an assessment of transient pressure gradient effects with respect to deformation is provided. 相似文献
942.
P F Chance B A Rabin S G Ryan Y Ding M Scavina B Crain J W Griffin D R Cornblath 《American journal of human genetics》1998,62(3):633-640
We performed genetic mapping studies of an 11-generation pedigree with an autosomal dominant, juvenile-onset motor-systems disease. The disorder is characterized by slow progression, distal limb amyotrophy, and pyramidal tract signs associated with severe loss of motor neurons in the brain stem and spinal cord. The gene for this disorder, classified as a form of juvenile amyotrophic lateral sclerosis (ALS), is designated "ALS4." We performed a genomewide search and detected strong evidence for linkage of the ALS4 locus to markers from chromosome 9q34. The highest LOD score (Z) was obtained with D9S1847 (Z=18.8, recombination fraction of .00). An analysis of recombinant events identified D9S1831 and D9S164 as flanking markers, on chromosome 9q34, that define an approximately 5-cM interval that harbors the ALS4 gene. These results extend the degree of heterogeneity within familial ALS syndromes, and they implicate a gene on chromosome 9q34 as critical for motor-neuron function. 相似文献
943.
Lacticin 3147, a Broad-Spectrum Bacteriocin Which Selectively Dissipates the Membrane Potential 总被引:14,自引:6,他引:8
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Olivia McAuliffe Maire P. Ryan R. Paul Ross Colin Hill Pieter Breeuwer Tjakko Abee 《Applied microbiology》1998,64(2):439-445
Lacticin 3147 is a broad-spectrum bacteriocin produced by Lactococcus lactis subsp. lactis DPC3147 (M. P. Ryan, M. C. Rea, C. Hill, and R. P. Ross, Appl. Environ. Microbiol. 62:612–619, 1996). Partial purification of the bacteriocin by hydrophobic interaction chromatography and reverse-phase fast protein liquid chromatography revealed that two components are required for full activity. Lacticin 3147 is bactericidal against L. lactis, Listeria monocytogenes, and Bacillus subtilis; at low concentrations of the bacteriocin, bactericidal activity is enhanced when target cells are energized. This finding suggests that the presence of a proton motive force promotes the interaction of the bacteriocin with the cytoplasmic membrane, leading to the formation of pores at these low lacticin 3147 concentrations. These pores were shown to be selective for K+ ions and inorganic phosphate. The loss of these ions resulted in immediate dissipation of the membrane potential and hydrolysis of internal ATP, leading to an eventual collapse of the pH gradient at the membrane and ultimately to cell death. Our results suggest that lacticin 3147 is a pore-forming bacteriocin which acts on a broad range of gram-positive bacteria. 相似文献
944.
Development of Bacterium-Based Heavy Metal Biosorbents: Enhanced Uptake of Cadmium and Mercury by Escherichia coli Expressing a Metal Binding Motif 总被引:5,自引:0,他引:5
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A gene coding for a de novo peptide sequence containing a metal binding motif was chemically synthesized and expressed in Escherichia coli as a fusion with the maltose binding protein. Bacterial cells expressing the metal binding peptide fusion demonstrated enhanced binding of Cd2+ and Hg2+ compared to bacterial cells lacking the metal binding peptide. The potential use of genetically engineered bacteria as biosorbents for the removal of heavy metals from wastewaters is discussed. 相似文献
945.
946.
Involvement of protein tyrosine phosphorylation in the effect of green tea polyphenols on Ehrlich ascites tumor cells in vitro 总被引:2,自引:0,他引:2
David Opare Kennedy Satomi Nishimura Tadayoshi Hasuma Yoshihisa Yano Shuzo Otani Isao Matsui-Yuasa 《Chemico-biological interactions》1998,110(3):645-172
Green tea extract and its polyphenolic components have been found to possess anticarcinogenic, antimutagenic, antihypertensive and antihepatotoxic effects, and several mechanisms have been proposed for these effects. In this study, the effects of five tea polyphenols, (−)-epigallocatechin-3-gallate (EGCG), (−)-epigallocatechin (EGC), (−) epicatechin-3-gallate (ECG), (−) epicatechin (EC) and (+)-catechin (C), were examined on the viability of Ehrlich ascites tumor cells in vitro and a possible relationship with tyrosine phosphorylation was determined. Proteins extracted from the cells treated with the tea polyphenols were separated by SDS-PAGE, and tyrosine-phosphorylated proteins were detected by immunoblotting with anti-phosphotyrosine antibody and the extent of phosphorylation determined. EGC (100 μM) caused a significant decrease in cell viability to 4.1±0.2% of the control value, and this correlated with a stimulation of protein tyrosine kinase (PTK) activity. EGCG (100 μM) also caused a slight decrease in cell viability (70% of the control value) but this and the other polyphenols, which had no effect on cell viability likewise, had no effect on tyrosine phosphorylation. Tyrosine phosphorylations of 42 and 45 kDa proteins were also observed for EGC. Further evaluation of the effect of EGC showed that the activity of ornithine decarboxylase (ODC), a key enzyme in polyamine biosynthesis in cells, decreased significantly as well. A significant correlation has therefore been observed between a cellular event, namely, a reduction in the viability of Ehrlich ascites tumor cells and an association with a tyrosine phosphorylation of 42 and 45 kDa proteins by the polyphenol EGC. 相似文献
947.
Effect of phosphorus supply on the formation and function of proteoid roots of white lupin (Lupinus albus L.) 总被引:11,自引:1,他引:10
G. Keerthisinghe P. J. Hocking P. R. Ryan & E. Delhaize 《Plant, cell & environment》1998,21(5):467-478
We investigated (1) the effect of constant and altered inorganic phosphate (Pi ) supply (1–100 mmol m–3 ) on proteoid root production by white lupin ( Lupinus albus L.); and (2) the variation in citrate efflux, enzyme activity and phosphate uptake along the proteoid root axis in solution culture. Proteoid root formation was greatest at Pi solution concentrations of 1–10 mmol m–3 and was suppressed at 25 mmol m–3 Pi and higher. Except at 1 mmol m–3 Pi , the formation of proteoid roots did not affect plant dry matter yields or shoot to root dry matter ratios, indicating that proteoid roots can form under conditions of adequate P supply and not at the expense of dry matter production. Plants with over 50% of the root system as proteoid roots had tissue P concentrations considered adequate for maximum growth, providing additional evidence that proteoid roots can form on P-sufficient plants. There was an inverse relationship between the Pi concentration in the youngest mature leaf and proteoid root formation. Citrate efflux and the activities of enzymes associated with citric acid synthesis (phosphoenolpyruvate carboxylase and malate dehydrogenase) varied along the proteoid root axis, being greatest in young proteoid rootlets of the 1–3 cm region from the root tip. Citrate release from the 0–1 and 5–9 cm regions of the proteoid root was only 7% (per unit root length) of that from the 1–3 cm segment. Electrical potential and 32 Pi uptake measurements showed that Pi uptake was more uniform along the proteoid root than citrate efflux. 相似文献
948.
949.
A field experiment was conducted to determine the seasonal patterns of arbuscular mycorrhiza (AM) in a dryland winter wheat
(Triticum aestivum L.) system and to determine wheat growth and P uptake responses to inoculation with mycorrhizal fungus. Broadcast-incorporated
treatments included (1) no inoculation with mycorrhizal fungus, with and without P fertilizer, and (2) mycorrhizal fungal
inoculation at a rate of 5000 spores of Glomus intraradices (Schenck and Smith), per 30 cm in each row, with and without fertilizer P. Winter wheat was seeded within a day after treatments
were imposed, and roots were sampled at five growth stages to quantify AM. Shoot samples were also taken for determination
of dry matter, grain yield and yield components, and N and P uptake. No AM infection was evident during the fall months following
seeding, which was characterized by low soil temperature, while during the spring, the AM increased gradually. Increases in
wheat grain yields by enhanced AM were of similar magnitude to the response obtained from P fertilization. However, responses
differed at intermediate growth stages. At the tillering stage, P uptake was mainly increased by P fertilization but not by
fungal inoculation. At harvest, enhanced AM increased P uptake regardless of whether or not fertilizer P was added. The AM
symbiosis increased with rising soil temperatures in the spring, in time to enhance late-season P accumulation and grain production.
Accepted: 15 July 1998 相似文献
950.
Matthew Kennedy Lian Yu Maria João Lima Carla S. Ascenso Christopher Czaja Isabel Moura Jose J. G. Moura F. Rusnak 《Journal of biological inorganic chemistry》1998,3(6):643-649
Desulforedoxin and the N-terminus of desulfoferrodoxin share a 36 amino acid domain containing a (Cys-S)4 metal binding site. Recombinant forms of desulforedoxin, an N-terminal fragment of desulfoferrodoxin, and two desulforedoxin
mutant proteins were reconstituted with Fe3+, Cd2+, and Zn2+ and relative metal ion affinities assessed by proton titrations. Protons compete with metal for protein ligands, a process
that can be followed by monitoring the optical spectrum of the metal-protein complex as a function of pH. For all polypeptides,
Fe3+ bound with the highest affinity, whereas the affinity of Zn2+ was greater than Cd2+ in desulforedoxin and the N-terminal fragment of desulfoferrodoxin, but this order was reversed in desulforedoxin mutant
proteins. Metal binding in both mutants was significantly impaired. Furthermore, the Fe3+ complex of both mutants underwent a time-dependent bleaching process which coincided with increased reactivity of cysteine
residues to Ellman's reagent and concomitant metal dissociation. It is hypothesized that this results from an autoredox reaction
in which Fe3+ is reduced to Fe2+ with attendant oxidation of ligand thiols.
Received: 17 June 1998 / Accepted: 3 September 1998 相似文献