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101.
Immunoglobulins couple the recognition of invading pathogens with the triggering of potent effector mechanisms for pathogen elimination. Different immunoglobulin classes trigger different effector mechanisms through interaction of immunoglobulin Fc regions with specific Fc receptors (FcRs) on immune cells. Here, we review the structural information that is emerging on three human immunoglobulin classes and their FcRs. New insights are provided, including an understanding of the antibody conformational adjustments that are required to bring effector cell and target cell membranes sufficiently close for efficient killing and signal transduction to occur. The results might also open up new possibilities for the design of therapeutic antibodies. 相似文献
102.
Burton MJ Mellor IR Duce IR Davies TG Field LM Williamson MS 《Insect biochemistry and molecular biology》2011,41(9):723-732
Knockdown resistance (kdr) in insects, caused by inherited nucleotide polymorphisms in the voltage-gated sodium channel (VGSC) gene, is a major threat to the efficacy of pyrethroid insecticides. Classic kdr, resulting from an L1014F substitution in the VGSC is now present in numerous pest species. Two other substitutions at the L1014 locus have also been reported, L1014S and L1014H. Here we have used expression of L1014 modified Drosophila para VGSCs in Xenopus oocytes with two-electrode voltage clamp to characterise all three mutations. The mutations L1014F and L1014H caused significant depolarizing shifts in the half activation voltage (V50,act) from −17.3 mV (wild-type) to −13.1 and −13.5 mV respectively, whereas L1014S caused no shift in V50,act but its currents decayed significantly faster than wild-type channels. Treatment of the wild-type channel with deltamethrin (≥1 nM), permethrin (≥30 nM) or DDT (≥1 ??M) resulted in hyperpolarizing shifts in V50,act. Deltamethrin, permethrin and DDT also produced “tail currents” with EC50s of 0.043, 0.40 and 65 ??M and maximum modifications of 837, 325 and 7% respectively. L1014F provided a high level of resistance against all insecticides for both measured parameters. L1014H most effectively combated deltamethrin induced tail currents while L1014S strongly resisted the large DDT induced shifts in V50,act. We conclude that L1014H and L1014S may have arisen through heavy exposure to specific pyrethroids and DDT respectively. 相似文献
103.
Bahiagrass,Corn, Cotton Rotations,and Pesticides for Managing Nematodes,Diseases, and Insects on Peanut 总被引:1,自引:0,他引:1
A. W. Johnson N. A. Minton T. B. Brenneman G. W. Burton A. K. Culbreath G. J. Gascho S. H. Baker 《Journal of nematology》1999,31(2):191-200
Florunner peanut was grown after 1 and 2 years of Tifton 9 bahiagrass, corn, cotton, and continuous peanut as whole-plots. Pesticide treatments aldicarb (3.4 kg a.i./ha), flutolanil (1.7 kg a.i./ha), aldicarb + flutolanil, and untreated (control) were sub-plots. Numbers of Meloidogyne arenaria second-stage juveniles in the soil and root-gall indices of peanut at harvest were consistently lower in plots treated with aldicarb and aldicarb + flutolanil than in flutolanil-treated and untreated plots. Percentages of peanut leaflets damaged by thrips and leafhoppers were consistently greater in flutolaniltreated and untreated plots than in plots treated with aldicarb or aldicarb + flutolanil but not affected by cropping sequences. Incidence of southern stem rot was moderate to high for all chemical treatments except those that included flutolanil. Stem rot loci were low in peanut following 2 years of bahiagrass, intermediate following 2 years of corn or cotton, and highest in continuous peanut. Rhizoctonia limb rot was more severe in the peanut monoculture than in peanut following 2 years of bahiagrass, corn, or cotton. Flutolanil alone or combined with aldicarb suppressed limb rot compared with aldicarb-treated and untreated plots. Peanut pod yields were 4,186 kg/ha from aldicarb + flutolanil-treated plots, 3,627 kg/ha from aldicarb-treated plots, 3,426 kg/ha from flutolanil-treated plots, and 3,056 kg/ha from untreated plots. Yields of peanut following 2 years of bahiagrass, corn, and cotton were 29% to 33% higher than yield of monocultured peanut. 相似文献
104.
STYLIANOS MICHAIL SIMAIAKIS EVEN TJØRVE GABRIELE GENTILE ALESSANDRO MINELLI MOISIS MYLONAS 《Biological journal of the Linnean Society. Linnean Society of London》2012,105(1):146-159
The present study article examines the shapes of centipede species–area relationships (SARs) in the Mediterranean islands, compares the results of the linear form of the power model between archipelagos, discusses biological significance of the power model parameters with other taxa on the Aegean archipelago, and tests for a significant small‐island effect (SIE). We used 11 models to test the SARs and we compared the quality‐of‐fit of all candidate models. The power function ranked first and Z‐values was in the range 0.106–0.334. We assessed the presence of SIEs by fitting both a continuous and discontinuous breakpoint regression model. The continuous breakpoint regression functions never performed much better than the closest discontinuous model as a predictor of centipede species richness. We suggest that the relatively low Z‐values in our data partly reflect better dispersal abilities in centipedes than in other soil invertebrate taxa. Longer periods of isolation and more recent island formation may explain the somewhat lower constant c in the western Mediterranean islands compared to the Aegean islands. Higher breakpoint values in the western Mediterranean may also be a result of larger distance to the mainland and longer separation times. Despite the differences in the geological history and the idiosyncratic features of the main island groups considered, the overall results are quite similar and this could be assigned to the ability of centipedes to disperse across isolation barriers. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 146–159. 相似文献
105.
Eight-carbon volatiles in mushrooms and fungi: properties, analysis, and biosynthesis 总被引:1,自引:0,他引:1
Eight-carbon volatiles are ubiquitous among fungi and characteristic of the fungal aroma. They are the product of the oxidation
and cleavage of the fatty acid linoleic acid and are classified as oxylipins, molecules taking part in a wide range of biological
processes. Their involvement in the fungal aroma, interactions with pests and pathogens, and reproductive events are reviewed
here, as well as the enzymic systems involved in their biosynthesis. 相似文献
106.
Developing cardiac myocytes divide a limited number of times before they stop and terminally differentiate, but the mechanism that stops their division is unknown. To help study the stopping mechanism, we defined conditions under which embryonic rat cardiac myocytes cultured in serum-free medium proliferate and exit the cell cycle on a schedule that closely resembles that seen in vivo. The culture medium contains FGF-1 and FGF-2, which stimulate cell proliferation, and thyroid hormone, which seems to be necessary for stable cell-cycle exit. Time-lapse video recording shows that the cells within a clone tend to divide a similar number of times before they stop, whereas cells in different clones divide a variable number of times before they stop. Cells cultured at 33 degrees C divide more slowly but stop dividing at around the same time as cells cultured at 37 degrees C, having undergone fewer divisions. Together, these findings suggest that an intrinsic timer helps control when cardiac myocytes withdraw from the cell cycle and that the timer does not operate by simply counting cell divisions. We provide evidence that the cyclin-dependent kinase inhibitors p18 and p27 may be part of the timer and that thyroid hormone may help developing cardiac myocytes stably withdraw from the cell cycle. 相似文献
107.
108.
Marian Wilson Samantha M. Riedy Maddy Himmel Ashley English Joshua Burton Sandra Albritton 《Chronobiology international》2018,35(6):849-852
ABSTRACTThis study assessed sleep quality, sleepiness and use of workplace break opportunities in 1285 health-care workers via an online questionnaire. Two hospitals were surveyed – one with and one without a fatigue mitigation policy. Across all respondents, 68.9% reported generally taking breaks of at least 30 min and 21.7% had access to a quiet place to rest, with no significant differences between hospitals. The presence of a fatigue mitigation policy was not associated with reduced sleepiness. However, accounting for hospital and shift characteristics, employees with access to a quiet place to rest while on break had significantly lower self-reported sleepiness scores. 相似文献
109.
James D. Burton Marianne K. Pedersen Harold D. Coble 《Journal of Plant Growth Regulation》2008,27(4):342-352
Cyclanilide is a plant growth regulator that is registered for use in cotton at different stages of growth, to either suppress
vegetative growth (in combination with mepiquat chloride) or accelerate senescence (enhance defoliation and boll opening,
used in combination with ethephon). This research was conducted to study the mechanism of action of cyclanilide: its potential
interaction with auxin (IAA) transport and signaling in plants. The activity of cyclanilide was compared with the activity
of the auxin transport inhibitors NPA and TIBA. Movement of [3H]IAA was inhibited in etiolated corn coleoptiles by 10 μM cyclanilide, NPA, and TIBA, which demonstrated that cyclanilide
affected polar auxin transport. Although NPA inhibited [3H]IAA efflux from cells in etiolated zucchini hypocotyls, cyclanilide had no effect. NPA did not inhibit the influx of IAA
into cells in etiolated zucchini hypocotyls, whereas cyclanilide inhibited uptake 25 and 31% at 10 and 100 μM, respectively.
Also, NPA inhibited the gravitropic response in tomato roots (85% at 1 μM) more than cyclanilide (30% at 1 μM). Although NPA
inhibited tomato root growth (30% at 1 μM), cyclanilide stimulated root growth (165% of control at 5 μM). To further characterize
cyclanilide action, plasma membrane fractions from etiolated zucchini hypocotyls were obtained and the binding of NPA, IAA,
and cyclanilide studied. Cyclanilide inhibited the binding of [3H]NPA and [3H]IAA with an IC50 of 50 μM for both. NPA did not affect the binding of IAA, nor did IAA affect the binding of NPA. Kinetic analysis indicated
that cyclanilide is a noncompetitive inhibitor of both NPA and IAA binding, with inhibition constants (K
i) of 40 and 2.3 μM, respectively. These data demonstrated that cyclanilide interacts with auxin-regulated processes via a
mechanism that is distinct from other auxin transport inhibitors. This research identifies a possible mechanism of action
for cyclanilide when used as a plant growth regulator. 相似文献
110.
Sediment quality criteria in use around the world 总被引:20,自引:0,他引:20
There have been numerous sediment quality guidelines (SQGs) developed during the past 20 years to assist regulators in dealing
with contaminated sediments. Unfortunately, most of these have been developed in North America. Traditionally, sediment contamination
was determined by assessing the bulk chemical concentrations of individual compounds and often comparing them with background
or reference values. Since the 1980s, SQGs have attempted to incorporate biological effects in their derivation approach.
These approaches can be categorized as empirical, frequency-based approaches to establish the relationship between sediment
contamination and toxic response, and theoretically based approaches that attempt to account for differences in bioavailability
through equilibrium partitioning (EqP) (i.e., using organic carbon or acid volatile sulfides). Some of these guidelines have
been adopted by various regulatory agencies in several countries and are being used as cleanup goals in remediation activities
and to identify priority polluted sites. The original SQGs, which compared bulk chemical concentrations to a reference or
to background, provided little insight into the ecosystem impact of sediment contaminants. Therefore, SQGs for individual
chemicals were developed that relied on field sediment chemistry paired with field or laboratory-based biological effects
data. Although some SQGs have been found to be relatively good predictors of significant site contamination, they also have
several limitations. False positive and false negative predictions are frequently in the 20% to 30% range for many chemicals
and higher for others. The guidelines are chemical specific and do not establish causality where chemical mixtures occur.
Equilibrium-based guidelines do not consider sediment ingestion as an exposure route. The guidelines do not consider spatial
and temporal variability, and they may not apply in dynamic or larger-grained sediments. Finally, sediment chemistry and bioavailability
are easily altered by sampling and subsequent manipulation processes, and therefore, measured SQGs may not reflect in situ
conditions. All the assessment tools provide useful information, but some (such as SQGs, laboratory toxicity and bioaccumulation,
and benthic indices) are prone to misinterpretation without the availability of specific in situ exposure and effects data.
SQGs should be used only in a “screening” manner or in a “weight-of-evidence” approach. Aquatic ecosystems (including sediments)
must be assessed in a “holistic” manner in which multiple components are assessed (e.g., habitat, hydrodynamics, resident
biota, toxicity, and physicochemistry, including SQGs) by using integrated approaches.
Received: December 26, 2000 / Accepted: December 28, 2001 相似文献