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141.
Controls on methane production in a tidal freshwater estuary and a peatland: methane production via acetate fermentation and CO2 reduction 总被引:2,自引:0,他引:2
G. Brooks Avery Robert D. Shannon Jeffrey R. White Christopher S. Martens Marc J. Alperin 《Biogeochemistry》2003,62(1):19-37
Rates of total methane production, acetate fermentation andCO2 reduction were compared for two different wetland sites. On aper-liter basis, sediments from the White Oak River estuary, a tidal freshwatersite in eastern North Carolina, had an annual methane production rate (53.3mMyr–1) an order of magnitude higher thanthat ofBuck Hollow Bog (5.5 mMyr–1), a peatlandinMichigan. Methane was produced in the White Oak River site on an annual basisbyboth acetate fermentation (72%) and CO2 reduction (28%) in a ratiotypical of freshwater methanogenic sites. Competition for acetate bynon-methanogenic microorganisms in Buck Hollow peat limited methane productionfrom acetate to only a few months a year, severely impacting annual methaneproduction rates. However, when acetate was available to the methanogens in thepeat during early spring, the percentage of methane production from acetatefermentation (84%) and CO2 reduction (16%) and rates of totalmethaneproduction were similar to those of the White Oak River sediments at the sametemperature. Rates of CO2 reduction and acetate fermentationconducted at both sites at various temperatures showed that Buck Hollow peatmethane production was also limited by a colder temperature regime as well asdifferences in the response of the CO2 reducing and aceticlasticmethanogens to temperature variations. 相似文献
142.
Marucci L Alpini G Glaser SS Alvaro D Benedetti A Francis H Phinizy JL Marzioni M Mauldin J Venter J Baumann B Ugili L LeSage G 《American journal of physiology. Gastrointestinal and liver physiology》2003,284(2):G290-G301
Bile acids are cytoprotective in hepatocytes by activating phosphatidylinositol-3-kinase (PI3-K) and its downstream signal AKT. Our aim was to determine whether feeding taurocholate to CCl(4)-treated rats reduces cholangiocyte apoptosis and whether this cytoprotective effect is dependent on PI3-K. Cholangiocyte proliferation, secretion, and apoptosis were determined in cholangiocytes from bile duct ligation (BDL), CCl(4)-treated BDL rats, and CCl(4)-treated taurocholate-fed rats. In vitro, we tested whether CCl(4) induces apoptosis and whether loss of cholangiocyte proliferation and secretion is dependent on PI3-K. The CCl(4)-induced cholangiocyte apoptosis and loss of cholangiocyte proliferation and secretion were reduced in CCl(4)-treated rats fed taurocholate. CCl(4)-induced cholangiocyte apoptosis, loss of cholangiocytes secretion, and proliferation were prevented by preincubation with taurocholate. Taurocholate cytoprotective effects were ablated by wortmannin. Taurocholate prevented, in vitro, CCl(4)-induced decrease of phosphorylated AKT protein expression in cholangiocytes. The cytoprotective effects of taurocholate on CCl(4) effects on cholangiocyte proliferation and secretion were abolished by wortmannin. Taurocholate protects cholangiocytes from CCl(4)-induced apoptosis by a PI3-K-dependent mechanism. Bile acids are important in the prevention of drug-induced ductopenia in cholangiopathies. 相似文献
143.
144.
Rabinovich BA Shannon J Su RC Miller RG 《Journal of immunology (Baltimore, Md. : 1950)》2000,165(5):2390-2397
Exposure of primary T cell blasts to stress in the forms of heat, hydrogen peroxide, or high-density growth conditions resulted in a state of enhanced susceptibility to killing by syngeneic IL-2-activated NK cells or lymphokine-activated killer cells, but not to killing by CTL. Cytotoxicity was perforin mediated and was not due to decreased target expression of total MHC class I. The levels of stress used had little effect on cell viability. For thermal stress, sensitization increased with temperature, required a minimum exposure time, and disappeared when cells were given a long enough recovery time. Our data support a model that predicts that activated NK cells play a role in the immunosurveillance of nontransformed stressed cells in normal animals. 相似文献
145.
146.
Sol-gel trapping of functional intermediates of hemoglobin: geminate and bimolecular recombination studies 总被引:1,自引:0,他引:1
Khan I Shannon CF Dantsker D Friedman AJ Perez-Gonzalez-de-Apodaca J Friedman JM 《Biochemistry》2000,39(51):16099-16109
The encapsulation of proteins in porous sol-gels is a promising technique for generating, trapping, and probing functionally significant nonequilibrium protein species. An essential step needed in the pursuit of that goal is establishing the degree to which the sol-gel limits conformational change upon adding or removing substrates. In the present study, geminate recombination and solvent phase bimolecular recombination of CO to human adult hemoglobin (HbA) are used as sensitive probes of the degree of conformational constraint within the sol-gel. Two forms of CO saturated encapsulated HbA are generated. In one case, designated [COHbA], the equilibrium form of COHbA is directly encapsulated. In the second case, designated as [deoxyHbA] + CO, the equilibrium form of deoxyHbA is encapsulated and only after the sample has aged is CO introduced to the HbA through the porous sol-gel matrix. Three different preparative protocols are used to generate the sol-gels for each of the two forms of encapsulated COHbA. The kinetic traces obtained from these encapsulated samples allow for an easy evaluation of the extent to which the sol-gel is locking in the initial tertiary/quaternary structure. The results show that the sol-gel encapsulated samples can be used with pulsed laser sources and that one of the tested encapsulation protocols is far superior with respect to conformational locking. This protocol is used to trap and probe nonequilibrium forms such as the liganded T state of HbA, a species whose properties are needed to fully explore allostery in HbA. 相似文献
147.
In this study, passive Ca2+ binding was determined in ventricular homogenates (VH) from neonatal (4–6 days) and adult rats, as well as in digitonin-permeabilized adult ventricular myocytes. Ca2+ binding sites, both endogenous and exogenous (Indo-1 and BAPTA) were titrated. Sarcoplasmic reticulum and mitochondrial Ca2+ uptake were blocked by thapsigargin and Ru360, respectively. Free [Ca2+] ([Ca2+]F was measured with Indo-1 and bound Ca2+ ([Ca2+]B) was the difference between [Ca2+]F and total Ca2+. Apparent Ca2+ dissociation constants (Kd) for BAPTA and Indo-1 were increased by 10–20 mg VH protein/ml (from 0.35 to 0.92 μM for Indo-1 and from 0.20 to 0.76 μM for BAPTA) and also by ruthenium red in the case of Indo-1. Titration with successive CaCl2 additions (2.5–10 nmoles) yielded δ[Ca2+]B/δ[Ca2+]F for the sum of [Ca2+]B at all three classes of binding sites. From this function, the apparent number of endogenous sites (Ben) and their Kd (Ken) were determined. Similar Ken values were obtained in neonatal and adult VH, as well as in adult myocytes (0.68 ± 0.14 μM, 0.69 ± 0.13 μM and 0.53 ± 0.10 μM, respectively). However, Ben was significantly higher in adult myocytes than in adult VH (1.73 ± 0.35 versus 0.70 ± 0.12 nmol/mg protein, P < 0.01), which correspond to ∼300 and 213 μmol/l cytosol. This indicates that binding sites are more concentrated in myocytes than in other ventricular components and that Ben determined in VH underestimates cellular Ben by 29%. Although Ben values in nmol/mg protein were similar in adult and neonatal VH (0.69 ± 0.12), protein content was much higher in adult ventricle (125 ± 7 versus 80 ± 1 mg protein/g wet weight, P < 0.01). Expressing Ben per unit cell volume (accounting for fractional mitochondrial volume, and 29% dilution in homogenate), the passive Ca2+ binding capacity at high-affinity sites is ∼300 and 176 mmol/I cytosol in adult and neonatal rat ventricular myocytes, respectively. Additional estimates suggest that passive Ca2+ buffering capacity in rat ventricle increases markedly during the first two weeks of life and that adult levels are attained by the end of the first month. 相似文献
148.
J Frank S Sinclair S Hogg-Johnson H Shannon C Bombardier D Beaton D Cole 《CMAJ》1998,158(12):1625-1631
Despite the publication in the mid-1990s of comprehensive practice guidelines for the management of acute low-back pain, both in the United States and elsewhere, this ubiquitous health problem continues to be the main cause of workers'' compensation claims in much of the Western world. This paper represents a synthesis of the intervention studies published in the last 4 years and is based on a new approach to categorizing these studies that emphasizes the stage or phase of back pain at the time of intervention and the site or agent of the intervention. Current thinking suggests that medical management in the first 3-4 weeks after the onset of pain should be generally conservative. Several studies of rather heterogeneous interventions focusing on return to work and implemented in the subacute stage (3-4 to 12 weeks after the onset of pain) have shown important reductions in time lost from work (by 30% to 50%). There is substantial evidence indicating that employers who promptly offer appropriately modified duties can reduce time lost per episode of back pain by at least 30%, with frequent spin-off effects on the incidence of new back-pain claims as well. Finally, newer studies of guidelines-based approaches to back pain in the workplace suggest that a combination of all these approaches, in a coordinated workplace-linked care system, can achieve a reduction of 50% in time lost due to back pain, at no extra cost and, in some settings, with significant savings. 相似文献
149.
Charles L. Shannon 《Anthropology & education quarterly》1999,30(3):387-389
Paths to Success: Beating the Odds in American Society. Charles C. Harrington and Susan K. Boardman, eds. Cambridge, MA: Harvard University Press, 1997. 238 pp. 相似文献
150.
Kyle K Biggar Cheng-Wei Wu Shannon N Tessier Jing Zhang Fabien Pifferi Martine Perret Kenneth B Storey 《基因组蛋白质组与生物信息学报(英文版)》2015,13(2):81-90
Very few selected species of primates are known to be capable of entering torpor. This exciting discovery means that the ability to enter a natural state of dormancy is an ancestral trait among primate... 相似文献