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1.
Evidence for Iron-Dependent Nitrate Respiration in the Dissimilatory Iron-Reducing Bacterium Geobacter metallireducens
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The dissimilatory iron-reducing bacterium Geobacter metallireducens was found to require iron at a concentration in excess of 50 μM for continuous cultivation on nitrate. Growth yield (~3-fold), cytochrome c content (~7-fold), and nitrate (~4.5-fold) and nitrite (~70-fold) reductase activities were all increased significantly when the growth medium was amended with 500 μM iron. 相似文献
2.
Beatriz Escudero Daniel Lucas Carmen Albo Suveera Dhup Jeff W. Bacher Aránzazu Sánchez-Mu?oz Margarita Fernández José Rivera-Torres Rosa M. Carmona Encarnación Fuster Candelas Carreiro Raquel Bernad Manuel A. González Vicente Andrés Luis Blanco Enrique Roche Isabel Fabregat Enrique Samper Antonio Bernad 《PloS one》2014,9(4)
3.
Herpes simplex virus 2 (HSV-2) 0ΔNLS is a live HSV-2 ICP0
- mutant vaccine strain that is profoundly attenuated in vivo due to its interferon-hypersensitivity. Recipients of the HSV-2 0ΔNLS vaccine are resistant to high-dose HSV-2 challenge as evidenced by profound reductions in challenge virus spread, shedding, disease and mortality. In the current study, we investigated the requirements for HSV-2 0ΔNLS vaccine-induced protection. Studies using (UV)-inactivated HSV-2 0ΔNLS revealed that self-limited replication of the attenuated virus was required for effective protection from vaginal or ocular HSV-2 challenge. Diminished antibody responses in recipients of the UV-killed HSV-2 vaccine suggested that antibodies might be playing a critical role in early protection. This hypothesis was investigated in B-cell-deficient μMT mice. Vaccination with live HSV-2 0ΔNLS induced equivalent CD8+ T cell responses in wild-type and μMT mice. Vaccinated μMT mice shed ~40-fold more infectious HSV-2 at 24 hours post-challenge relative to vaccinated wild-type (B-cell+) mice, and most vaccinated μMT mice eventually succumbed to a slowly progressing HSV-2 challenge. Importantly, passive transfer of HSV-2 antiserum restored full protection to HSV-2 0ΔNLS-vaccinated μMT mice. The results demonstrate that B cells are required for complete vaccine-induced protection against HSV-2, and indicate that virus-specific antibodies are the dominant mediators of early vaccine-induced protection against HSV-2. 相似文献
4.
A. David McKinnon Jason Doyle Samantha Duggan Murray Logan Christian L?nborg Richard Brinkman 《PloS one》2015,10(10)
The specific activity of aminoacyl-tRNA synthetases (spAARS), an index of growth rate, and of the electron transport system (spETS), an index of respiration, was measured in three size fractions (73–150 μm, >150 μm and >350 μm) of zooplankton during five cruises to tropical coastal waters of the Kimberley coast (North West Australia) and four cruises to waters of the Great Barrier Reef (GBR; North East Australia). The N-specific biomass of plankton was 3–4-fold higher in the Kimberley than on the GBR in all 3 size classes: Kimberley 1.27, 3.63, 1.94 mg m-3; GBR 0.36, 0.88 and 0.58 mg m-3 in the 73–150 μm, >150 μm and >350 μm size classes, respectively. Similarly, spAARS activity in the Kimberley was greater than that of the GBR: 88.4, 132.2, and 147.6 nmol PPi hr-1 mg protein -1 in the Kimberley compared with 71.7, 82.0 and 83.8 nmol PPi hr-1 mg protein -1 in the GBR, for the 73–150 μm, >150 μm and >350 μm size classes, respectively. Specific ETS activity showed similar differences in scale between the two coasts: 184.6, 148.8 and 92.2 μL O2 hr-1 mg protein-1 in the Kimberley, against 86.5, 88.3 and 71.3 μL O2 hr-1 mg protein-1 in the GBR. On the basis of these measurements, we calculated that >150 μm zooplankton grazing accounted for 7% of primary production in the Kimberley and 8% in GBR waters. Area-specific respiration by >73 μm zooplankton was 7-fold higher in the Kimberley than on the GBR and production by >150 μm zooplankton was of the order of 278 mg C m-2 d-1 in the Kimberley and 42 mg C m-2 d-1 on the GBR. We hypothesize that the much stronger physical forcing on the North West shelf is the principal driver of higher rates in the west than in the east of the continent. 相似文献
5.
Extracellular Polysaccharide Is Not Responsible for Aluminum Tolerance of Rhizobium leguminosarum bv. Phaseoli CIAT899 总被引:2,自引:1,他引:1
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Strain UHM-5, a pSym- Exo- derivative of the aluminum-tolerant Rhizobium leguminosarum bv. phaseoli strain CIAT899, was equally tolerant of aluminum (Al) as the parental culture. Dialyzed culture supernatants of the wild-type cells grown in YEM broth (109 cells ml-1) contained 185 μg of glucose equivalents ml-1 whereas UHM-5 culture supernatants yielded 2 μg of glucose ml-1. The Exo- derivative and the parental strain gave essentially similar growth in medium containing from 0 to 300 μM Al, indicating that the pSym of CIAT899, and extracellular polysaccharide, were not involved in the aluminum tolerance of this strain. However, increasing the level of Al from 80 to 150 μM increased the lag phase, induced a slight killing of the inoculum, and depressed the final populations by about fivefold. Doubling the aluminum concentration from 150 to 300 μM presented a severe aluminum stress to CIAT899 and UHM-5: the inoculum level dropped 10-fold, indicating killing of the inoculum, and remained depressed for ca. 4 days before continuing to grow slowly; the final population was decreased 15-fold relative to that of cultures grown in medium containing 80 μM Al. The production by CIAT899 of other extracellular or intracellular aluminum tolerance factors was investigated in culture by using aluminum-sensitive rhizobia as stress indicators. These experiments, conducted at 80 μM Al, demonstrated that CIAT899 produced neither extracellular nor intracellular products that could alleviate toxicity for the Al-sensitive indicator rhizobia. 相似文献
6.
Hsuan-Fu Kuo Yan-Jie Lai Jung-Chou Wu Kun-Tai Lee Chih-Sheng Chu Ing-Jun Chen Jiunn-Ren Wu Bin-Nan Wu 《International journal of biological sciences》2014,10(1):64-72
This study investigated whether KMUP-1, a xanthine-derivative K+ channel opener, could prevent serotonin-induced hypertrophy in H9c2 cardiomyocytes via L-type Ca2+ channels (LTCCs). Rat heart-derived H9c2 cells were incubated with serotonin (10 μM) for 4 days. The cell size increased by 155.5%, and this was reversed by KMUP-1 (≥1 μM), and attenuated by the LTCC blocker verapamil (1 μM) and the 5-HT2A antagonist ketanserin (0.1 μM), but unaffected by the 5-HT2B antagonist SB206553. A perforated whole-cell patch-clamp technique was used to investigate Ca2+ currents through LTCCs in serotonin-induced H9c2 hypertrophy, in which cell capacitance and current density were increased. The LTCC current (ICa,L) increased ~2.9-fold in serotonin-elicited H9c2 hypertrophy, which was attenuated by verapamil and ketanserin, but not affected by SB206553 (0.1 μM). Serotonin-increased ICa,L was reduced by KMUP-1, PKA and PKC inhibitors (H-89, 1 μM and chelerythrine, 1 μM) while the current was enhanced by the PKC activator PMA, (1 μM) but not the PKA activator 8-Br-cAMP (100 μM), and was abolished by KMUP-1. In contrast, serotonin-increased ICa,L was blunted by the PKG activator 8-Br-cGMP (100 μM), but unaffected by the PKG inhibitor KT5823 (1 μM). Notably, KMUP-1 blocked serotonin-increased ICa,L but this was partially reversed by KT5823. In conclusion, serotonin-increased ICa,L could be due to activated 5-HT2A receptor-mediated PKA and PKC cascades, and/or indirect interaction with PKG. KMUP-1 prevents serotonin-induced H9c2 cardiomyocyte hypertrophy, which can be attributed to its PKA and PKC inhibition, and/or PKG stimulation. 相似文献
7.
New activated sludge processes that utilize sorption as a major mechanism for organics removal are being developed to maximize energy recovery from wastewater organics, or as enhanced primary treatment technologies. To model and optimize sorption-based activated sludge processes, further knowledge about sorption of organics onto sludge is needed. This study compared primary-, anaerobic-, and aerobic activated sludge as sorbents, determined sorption capacity and kinetics, and investigated some characteristics of the organics being sorbed. Batch sorption assays were carried out without aeration at a mixing velocity of 200 rpm. Only aerobic activated sludge showed net sorption of organics. Sorption of dissolved organics occurred by a near-instantaneous sorption event followed by a slower process that obeyed 1st order kinetics. Sorption of particulates also followed 1st order kinetics but there was no instantaneous sorption event; instead there was a release of particles upon mixing. The 5-min sorption capacity of activated sludge was 6.5±10.8 mg total organic carbon (TOC) per g volatile suspend solids (VSS) for particulate organics and 5.0±4.7 mgTOC/gVSS for dissolved organics. The observed instantaneous sorption appeared to be mainly due to organics larger than 20 kDa in size being sorbed, although molecules with a size of about 200 Da with strong UV absorbance at 215–230 nm were also rapidly removed. 相似文献
8.
A New Sensitive Bioassay for Determination of Microbially Available Phosphorus in Water 总被引:18,自引:3,他引:15
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Markku J. Lehtola Ilkka T. Miettinen Terttu Vartiainen Pertti J. Martikainen 《Applied microbiology》1999,65(5):2032-2034
The content of assimilable organic carbon has been proposed to control the growth of microbes in drinking water. However, recent results have shown that there are regions where it is predominantly phosphorus which determines the extent of microbial growth in drinking waters. Even a very low concentration of phosphorus (below 1 μg of P liter−1) can promote extensive microbial growth. We present here a new sensitive method to determine microbially available phosphorus concentrations in water down to 0.08 μg of P liter−1. The method is a bioassay in which the analysis of phosphorus in a water sample is based on maximum growth of Pseudomonas fluorescens P17 when the energy supply and inorganic nutrients, with the exception of phosphorus, do not limit bacterial growth. Maximum growth (CFU) in the water sample is related to the concentration of phosphorus with the factor 373,200 ± 9,400 CFU/μg of PO4-P. A linear relationship was found between cell growth and phosphorus concentration between 0.05 to 10 μg of PO4-P liter−1. The content of microbially available phosphorus in Finnish drinking waters varied from 0.1 to 10.2 μg of P liter−1 (median, 0.60 μg of P liter−1). 相似文献
9.
Due to its unique location, the endothelial surface glycocalyx (ESG) at the luminal side of the microvessel wall may serve as a mechano-sensor and transducer of blood flow and thus regulate endothelial functions. To examine this role of the ESG, we used fluorescence microscopy to measure nitric oxide (NO) production in post-capillary venules and arterioles of rat mesentery under reduced (low) and normal (high) flow conditions, with and without enzyme pretreatment to remove heparan sulfate (HS) of the ESG and in the presence of an endothelial nitric oxide synthase (eNOS) inhibitor, NG-monomethyl-L-arginine (L-NMMA). Rats (SD, 250–300g) were anesthetized. The mesentery was gently taken out from the abdominal cavity and arranged on the surface of a glass coverslip for the measurement. An individual post-capillary venule or arteriole was cannulated and loaded for 45 min with 5 μM 4, 5-Diaminofluorescein diacetate, a membrane permeable fluorescent indictor for NO, then the NO production was measured for ~10 min under a low flow (~300 μm/s) and for ~60 min under a high flow (~1000 μm/s). In the 15 min after switching to the high flow, DAF-2-NO fluorescence intensity increased to 1.27-fold of its baseline, DAF-2-NO continuously increased under the high flow, to 1.53-fold of its baseline in 60 min. Inhibition of eNOS by 1 mM L-NMMA attenuated the flow-induced NO production to 1.13-fold in 15 min and 1.30-fold of its baseline in 60 min, respectively. In contrast, no significant increase in NO production was observed after switching to the high flow for 60 min when 1 h pretreatment with 50 mU/mL heparanase III to degrade the ESG was applied. Similar NO production was observed in arterioles under low and high flows and under eNOS inhibition. Our results suggest that ESG participates in endothelial cell mechanosensing and transduction through its heparan sulfate to activate eNOS. 相似文献
10.
Carbon gain and photosynthetic response of chrysanthemum to photosynthetic photon flux density cycles
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Most models of carbon gain as a function of photosynthetic irradiance assume an instantaneous response to increases and decreases in irradiance. High- and low-light-grown plants differ, however, in the time required to adjust to increases and decreases in irradiance. In this study the response to a series of increases and decreases in irradiance was observed in Chrysanthemum × morifolium Ramat. “Fiesta” and compared with calculated values assuming an instantaneous response. There were significant differences between high- and low-light-grown plants in their photosynthetic response to four sequential photosynthetic photon flux density (PPFD) cycles consisting of 5-minute exposures to 200 and 400 micromoles per square meter per second (μmol m−2s−1). The CO2 assimilation rate of high-light-grown plants at the cycle peak increased throughout the PPFD sequence, but the rate of increase was similar to the increase in CO2 assimilation rate observed under continuous high-light conditions. Low-light leaves showed more variability in their response to light cycles with no significant increase in CO2 assimilation rate at the cycle peak during sequential cycles. Carbon gain and deviations from actual values (percentage carbon gain over- or underestimation) based on assumptions of instantaneous response were compared under continuous and cyclic light conditions. The percentage carbon gain overestimation depended on the PPFD step size and growth light level of the leaf. When leaves were exposed to a large PPFD increase, the carbon gain was overestimated by 16 to 26%. The photosynthetic response to 100 μmol m−2 s−1 PPFD increases and decreases was rapid, and the small overestimation of the predicted carbon gain, observed during photosynthetic induction, was almost entirely negated by the carbon gain underestimation observed after a decrease. If the PPFD cycle was 200 or 400 μmol m−2 s−1, high- and low-light leaves showed a carbon gain overestimation of 25% that was not negated by the underestimation observed after a light decrease. When leaves were exposed to sequential PPFD cycles (200-400 μmol m−2 s−1), carbon gain did not differ from leaves exposed to a single PPFD cycle of identical irradiance integral that had the same step size (200-400-200 μmol m−2 s−1) or mean irradiance (200-300-200 μmol m−2 s−1). 相似文献
11.
Bowsher CG Ferrie BJ Ghosh S Todd J Thompson JE Rothstein SJ 《Plant physiology》1992,100(4):1802-1807
Membrane-associated lipoxygenase from green tomato (Lycopersicon esculentum L. cv Caruso) fruit has been purified 49-fold to a specific activity of 8.3 μmol·min−1·mg−1 of protein by solubilization of microsomal membranes with Triton X-100, followed by anion- exchange and size-exclusion chromatography. The apparent molecular mass of the enzyme was estimated to be 97 and 102 kD by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and size-exclusion chromatography, respectively. The purified membrane lipoxygenase preparation consisted of a single major band following sodium dodecyl sulfate-polyacrylamide gel electrophoresis, which cross-reacts with immunoserum raised against soluble soybean lipoxygenase 1. It has a pH optimum of 6.5, an apparent Km of 6.2 μm, and Vmax of 103. μmol·min−1·mg−1 of protein with linoleic acid as substrate. Corresponding values for the partially purified soluble lipoxygenase from tomato are 3.8 μm and 1.3 μmol·min−1·mg−1 of protein, respectively. Thus, the membrane-associated enzyme is kinetically distinguishable from its soluble counterpart. Sucrose density gradient fractionation of the isolated membranes indicated that the membrane-associated lipoxygenase sediments with thylakoids. A lipoxygenase band with a corresponding apparent mol wt of 97,000 was identified immunologically in sodium dodecyl sulfate-polyacrylamide gel electrophoresis-resolved proteins of purified thylakoids prepared from intact chloroplasts isolated from tomato leaves and fruit. 相似文献
12.
We investigated the effects of temperature on white adipocyte exocytosis (measured as increase in membrane capacitance) and short-term adiponectin secretion with the aim to elucidate mechanisms important in regulation of white adipocyte stimulus-secretion coupling. Exocytosis stimulated by cAMP (included in the pipette solution together with 3 mM ATP) in the absence of Ca2+ (10 mM intracellular EGTA) was equal at all investigated temperatures (23°C, 27°C, 32°C and 37°C). However, the augmentation of exocytosis induced by an elevation of the free cytosolic [Ca2+] to ~1.5 μM (9 mM Ca2+ + 10 mM EGTA) was potent at 32°C or 37°C but less distinct at 27°C and abolished at 23°C. Adiponectin secretion stimulated by 30 min incubations with the membrane permeable cAMP analogue 8-Br-cAMP (1 mM) or a combination of 10 μM forskolin and 200 μM IBMX was unaffected by a reduction of temperature from 32°C to 23°C. At 32°C, cAMP-stimulated secretion was 2-fold amplified by inclusion of the Ca2+ ionophore ionomycin (1μM), an effect that was not observed at 23°C. We suggest that cooling affects adipocyte exocytosis/adiponectin secretion at a Ca2+-dependent step, likely involving ATP-dependent processes, important for augmentation of cAMP-stimulated adiponectin release. 相似文献
13.
Ferrous Iron-Dependent Volatilization of Mercury by the Plasma Membrane of Thiobacillus ferrooxidans
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Kenji Iwahori Fumiaki Takeuchi Kazuo Kamimura Tsuyoshi Sugio 《Applied microbiology》2000,66(9):3823-3827
Of 100 strains of iron-oxidizing bacteria isolated, Thiobacillus ferrooxidans SUG 2-2 was the most resistant to mercury toxicity and could grow in an Fe2+ medium (pH 2.5) supplemented with 6 μM Hg2+. In contrast, T. ferrooxidans AP19-3, a mercury-sensitive T. ferrooxidans strain, could not grow with 0.7 μM Hg2+. When incubated for 3 h in a salt solution (pH 2.5) with 0.7 μM Hg2+, resting cells of resistant and sensitive strains volatilized approximately 20 and 1.7%, respectively, of the total mercury added. The amount of mercury volatilized by resistant cells, but not by sensitive cells, increased to 62% when Fe2+ was added. The optimum pH and temperature for mercury volatilization activity were 2.3 and 30°C, respectively. Sodium cyanide, sodium molybdate, sodium tungstate, and silver nitrate strongly inhibited the Fe2+-dependent mercury volatilization activity of T. ferrooxidans. When incubated in a salt solution (pH 3.8) with 0.7 μM Hg2+ and 1 mM Fe2+, plasma membranes prepared from resistant cells volatilized 48% of the total mercury added after 5 days of incubation. However, the membrane did not have mercury reductase activity with NADPH as an electron donor. Fe2+-dependent mercury volatilization activity was not observed with plasma membranes pretreated with 2 mM sodium cyanide. Rusticyanin from resistant cells activated iron oxidation activity of the plasma membrane and activated the Fe2+-dependent mercury volatilization activity of the plasma membrane. 相似文献
14.
Bangtian Xu Tingting Tong Xin Wang Fang Liu Xiang Zhang Xiaolei Hu Xinpeng Li Xiaolan Yang Fei Liao 《Journal of enzyme inhibition and medicinal chemistry》2022,37(1):728
The linking of ethacrynic acid with ethylenediamine and 1,4-butanediamine gave EDEA and BDEA, respectively, as membrane-permeable divalent pro-inhibitors of glutathione S-transferase (GST). Their divalent glutathione conjugates showed subnanomolar inhibition and divalence-binding to GSTmu (GSTM) (PDB: 5HWL) at ∼0.35 min−1. In cisplatin-resistant SK-OV-3, COC1, SGC7901 and A549 cells, GSTM activities probed by 15 nM BDEA or EDEA revealed 5-fold and 1.0-fold increases in cisplatin-resistant SK-OV-3 and COC1 cells, respectively, in comparison with the susceptible parental cells. Being tolerable by HEK293 and LO2 cells, BDEA at 0.2 μM sensitised resistant SK-OV-3 and COC1 cells by ∼3- and ∼5-folds, respectively, released cytochrome c and increased apoptosis; EDEA at 1.0 μM sensitised resistant SK-OV-3 and A549 cells by ∼5- and ∼7-fold, respectively. EDEA at 1.7 μg/g sensitised resistant SK-OV-3 cells to cisplatin at 3.3 μg/g in nude mouse xenograft model. BDEA and EDEA are promising leads for probing cellular GSTM and sensitising cisplatin-resistant ovarian cancers. 相似文献
15.
Electrotransformation of several strains of Clostridium thermocellum was achieved using plasmid pIKm1 with selection based on resistance to erythromycin and lincomycin. A custom-built pulse generator was used to apply a square 10-ms pulse to an electrotransformation cuvette consisting of a modified centrifuge tube. Transformation was verified by recovery of the shuttle plasmid pIKm1 from presumptive transformants of C. thermocellum with subsequent PCR specific to the mls gene on the plasmid, as well as by retransformation of Escherichia coli. Optimization carried out with strain DSM 1313 increased transformation efficiencies from <1 to (2.2 ± 0.5) × 105 transformants per μg of plasmid DNA. Factors conducive to achieving high transformation efficiencies included optimized periods of incubation both before and after electric pulse application, chilling during cell collection and washing, subculture in the presence of isoniacin prior to electric pulse application, a custom-built cuvette embedded in an ice block during pulse application, use of a high (25-kV/cm) field strength, and induction of the mls gene before plating the cells on selective medium. The protocol and preferred conditions developed for strain DSM 1313 resulted in transformation efficiencies of (5.0 ± 1.8) × 104 transformants per μg of plasmid DNA for strain ATCC 27405 and ~1 × 103 transformants per μg of plasmid DNA for strains DSM 4150 and 7072. Cell viability under optimal conditions was ~50% of that of controls not exposed to an electrical pulse. Dam methylation had a beneficial but modest (7-fold for strain ATCC 27405; 40-fold for strain DSM 1313) effect on transformation efficiency. The effect of isoniacin was also strain specific. The results reported here provide for the first time a gene transfer method functional in C. thermocellum that is suitable for molecular manipulations involving either the introduction of genes associated with foreign gene products or knockout of native genes. 相似文献
16.
Cocultivation of avian orthomyxoviruses and paramyxoviruses in embryonated eggs: implications for surveillance studies.
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A relatively inexpensive flow microcalorimeter is described which is capable of detecting heat outputs as low as 3 μW (precision, ±2%). Its use is illustrated on river epilithon (0.8 to 6.8 μW cm−2), river sand (9.8 μW cm−3), and marine sand (15.3 μW cm−3); however, it could be used to detect the heat output from any biotic material over which a flow of water can be passed, provided that such an action would not be disruptive to chemical and biological equilibria. 相似文献
17.
Abhay P. Sagare Robert D. Bell Alaka Srivastava Jesse D. Sengillo Itender Singh Yoichiro Nishida Nienwen Chow Berislav V. Zlokovic 《The Journal of biological chemistry》2013,288(21):15154-15166
Soluble low density lipoprotein receptor-related protein-1 (sLRP1) binds ∼70% of amyloid β-peptide (Aβ) in human plasma. In Alzheimer disease (AD) and individuals with mild cognitive impairment converting to AD, plasma sLRP1 levels are reduced and sLRP1 is oxidized, which results in diminished Aβ peripheral binding and higher levels of free Aβ in plasma. Experimental studies have shown that free circulating Aβ re-enters the brain and that sLRP1 and/or its recombinant wild type cluster IV (WT-LRPIV) prevent Aβ from entering the brain. Treatment of Alzheimer APPsw+/0 mice with WT-LRPIV has been shown to reduce brain Aβ pathology. In addition to Aβ, LRPIV binds multiple ligands. To enhance LRPIV binding for Aβ relative to other LRP1 ligands, we generated a library of LRPIV-derived fragments and full-length LRPIV variants with glycine replacing aspartic acid residues 3394, 3556, and 3674 in the calcium binding sites. Compared with WT-LRPIV, a lead LRPIV-D3674G mutant had 1.6- and 2.7-fold higher binding affinity for Aβ40 and Aβ42 in vitro, respectively, and a lower binding affinity for other LRP1 ligands (e.g. apolipoprotein E2, E3, and E4 (1.3–1.8-fold), tissue plasminogen activator (2.7-fold), matrix metalloproteinase-9 (4.1-fold), and Factor Xa (3.8-fold)). LRPIV-D3674G cleared mouse endogenous brain Aβ40 and Aβ42 25–27% better than WT-LRPIV. A 3-month subcutaneous treatment of APPsw+/0 mice with LRPIV-D3674G (40 μg/kg/day) reduced Aβ40 and Αβ42 levels in the hippocampus, cortex, and cerebrospinal fluid by 60–80% and improved cerebral blood flow responses and hippocampal function at 9 months of age. Thus, LRPIV-D3674G is an efficient new Aβ clearance therapy. 相似文献
18.
Steady-State Growth and Chemical Composition of the Marine Chlorophyte Dunaliella tertiolecta in Nitrogen-Limited Continuous Cultures 总被引:2,自引:2,他引:0
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The marine chlorophyte Dunaliella tertiolecta was grown in continuous cultures under NH4+-N, NO2−-N, NO3−-N, and urea-N limitations. The effect of the nitrogen cell quota (Qn) on the steady-state growth rate (μ) was the same regardless of the N source. The relationship between μ and Qn was well described by the Droop equation, but only up to the true maximum growth rate ^μ (= cell washout rate). The ratio between the minimum cell quota (kQ) and the maximum cell quota (Qm) was 0.19. Hence, there is no substitute for determining ^μ experimentally. That there was no difference in growth response to different N sources suggests that no internal pooling of inorganic nitrogen occurred. Both the carbon (Qc) and phosphorus (Qp) cell quotas under N limitation increased with increasing μ in a threshold fashion: virtually no change in either cell quota up to ~0.8 ^μ, followed by a rapid and large increase up to ^μ. In addition, in the region of low μ, there was an increase in Qp with a decreasing medium N/P ratio of between 15 and 5 (by atoms). The results generally indicate the physiological limits in cellular constituency under N limitation. The usefulness of this information, however, in describing the response of natural populations of marine phytoplankton to transient nutrient exposures on the temporal and spatial microscales that most likely exist is of limited value. 相似文献
19.
Bacterioplankton Secondary Production Estimates for Coastal Waters of British Columbia, Antarctica, and California 总被引:74,自引:46,他引:28
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The principal objective of this study was to quantify the rate of heterotrophic bacterioplankton production. Production was estimated by two approaches: (i) measurement of increasing bacterial abundance with time in filtered (3-μm pore size) seawater and (ii) estimation of bacterial deoxyribonucleic acid synthesis by tritiated thymidine incorporation in unfractionated seawater. The two approaches yielded comparable results when used at the Controlled Ecosystem Population Experiment (Saanich Inlet, British Columbia, Canada), at McMurdo Sound (Antarctica), and off Scripps Pier (La Jolla, Calif.). Estimated bacterioplankton production was lower in Antarctic samples (ranging from ~0 to 2.9 μg of C liter−1 day−1) than in those from the other two sites (ranging from 0.7 to 71 μg of C liter−1 day−1). In all three regions studied, it appeared that a significant fraction of the total primary production was utilized by the bacterioplankton and that substantial growth could occur in the absence of large particles. These results support the conclusion that bacterioplankton are a quantitatively important component of coastal marine food webs. 相似文献
20.
Lei Zhang Xueqi Wang Jingxin Chen Shaohu Sheng Thomas R. Kleyman 《The Journal of biological chemistry》2023,299(3)
Epithelial Na+ channels (ENaCs) and related channels have large extracellular domains where specific factors interact and induce conformational changes, leading to altered channel activity. However, extracellular structural transitions associated with changes in ENaC activity are not well defined. Using crosslinking and two-electrode voltage clamp in Xenopus oocytes, we identified several pairs of functional intersubunit contacts where mouse ENaC activity was modulated by inducing or breaking a disulfide bond between introduced Cys residues. Specifically, crosslinking E499C in the β-subunit palm domain and N510C in the α-subunit palm domain activated ENaC, whereas crosslinking βE499C with αQ441C in the α-subunit thumb domain inhibited ENaC. We determined that bridging βE499C to αN510C or αQ441C altered the Na+ self-inhibition response via distinct mechanisms. Similar to bridging βE499C and αQ441C, we found that crosslinking palm domain αE557C with thumb domain γQ398C strongly inhibited ENaC activity. In conclusion, we propose that certain residues at specific subunit interfaces form microswitches that convey a conformational wave during ENaC gating and its regulation. 相似文献