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1.
Studies on the enzymic synthesis of glutamine 总被引:17,自引:9,他引:8
ELLIOTT WH 《The Biochemical journal》1951,49(1):106-112
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SUMMARY. Larvae of Dixa , especially D. puberula Loew., were a significant component of the invertebrate drift in the Walla Brook in southwest England, the Wilfin Beck and the River Duddon in the English Lake District, and the River Estibère in the French Pyrenees. The drifting of the larvae increased markedly at night and showed a definite diel periodicity with maximum numbers usually in the early hours of the night. Seasonal peaks in the density of larvae in the drift frequently occurred in months when adults and especially pupae were present. Most drifting larvae were in the fourth and final instar, and their drift rate usually increased when they were searching for suitable pupation sites. 相似文献
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A comparative study of four dredges used for sampling benthic macroinvertebrates in rivers 总被引:1,自引:0,他引:1
SUMMARY. After considering the large number of dredges described in the literature, four light-weight dredges were chosen for manual operation from a small boat or the bank: Irish triangular dredge, small Fast dredge, medium-sized and large Naturalist's dredges. The dredges were tested in a series of trials at three sites in two rivers. A stratified random sample (number of sampling units, n = 5) was taken at each site and the modal particle sizes at sites 1–3 were 1–2 mm (fine gravel), 64–128 mm (larger stones) and 128–256 mm, respectively. The dredges usually took a similar range of stone sizes at each site but the design of the Fast dredge excluded larger stones (>16 mm). The Irish dredge sometimes failed to operate correctly. Variations in the volume of substrata taken with each dredge were large, both between sampling units in the same sample and between samples. The latter differences were partially due to the increase in the modal size of the stones, especially between sites 1 and 2, the different sampling areas of the dredges and the depth of penetration into the substratum. Penetration depth was probably greatest for the two Naturalist's dredges, smaller for the Fast dredge and smallest for the Irish dredge. In field trials, the relative abundances of major taxa were similar for most dredges at each site; major exceptions were the Fast dredge at site 2 and the Irish dredge at site 3. There was a high variability between sampling units in the same sample and therefore a lack of precision in the estimates of the mean number of invertebrates per sample. Therefore, the dredges cannot be used as quantitative samplers for the estimation of population density. Their adequacy as qualitative samplers for the estimation of total number of taxa per sample varied considerably and maximum estimates of their efficiencies for a small sample (n= 5) were <40% for the Irish and Fast dredges, >57% for the medium-sized Naturalist's dredge and >76% for the large Naturalist's dredge. There was a clear relationship between the number of taxa and the number of invertebrates taken at each site and this relationship was well described by a power law with an exponent within the range 0.18–0.53. The number of sampling units in the sample had no significant effect on the power-law equations for each site. The power-law equation was very similar for most of the dredges at each site, the only major exception being the Fast dredge at site 1. The implications of this relationship are discussed. 相似文献
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The biocontrol properties of Trichoderma species are well documented, but their effectiveness in antagonism of the problematic Sclerotium cepivorum, the causal agent of white rot in Allium species, appears limited with reports of significant control only relating to deliberately-mutated strains of Trichoderma. Our previous studies have indicated the possibility of using selected naturally-occurring strains of the antagonist in the suppression of other diseases; now in vitro and controlled environment in vivo studies have indicated that a degree of control of Onion White Rot is possible, and that the selected antagonist strains can be used in integrated treatments with Iprodione to good effect. The possible value of such treatments is considered in light of other approaches to the suppression of this continuing problem. 相似文献
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Karim M ElSawy Adelene Sim David P Lane Chandra S Verma Leo SD Caves 《Cell cycle (Georgetown, Tex.)》2015,14(2):179-188
The interaction of p53 and MDM2 is modulated by the phosphorylation of p53. This mechanism is key to activating p53, yet its molecular determinants are not fully understood. To study the spatiotemporal characteristics of this molecular process we carried out Brownian dynamics simulations of the interactions of the MDM2 protein with a p53 peptide in its wild type state and when phosphorylated at Thr18 (pThr18) and Ser20 (pSer20). We found that p53 phosphorylation results in concerted changes in the topology of the interaction landscape in the diffusively bound encounter complex domain. These changes hinder phosphorylated p53 peptides from binding to MDM2 well before reaching the binding site. The underlying mechanism appears to involve shift of the peptide away from the vicinity of the MDM2 protein, peptide reorientation, and reduction in peptide residence time relative to wild-type p53 peptide. pThr18 and pSr20 p53 peptides experience reduction in residence times by factors of 13.6 and 37.5 respectively relative to the wild-type p53 peptide, indicating a greater role for Ser20 phosphorylation in abrogating p53 MDM2 interactions. These detailed insights into the effect of phosphorylation on molecular interactions are not available from conventional experimental and theoretical approaches and open up new avenues that incorporate molecular interaction dynamics, for stabilizing p53 against MDM2, which is a major focus of anticancer drug lead development. 相似文献