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排序方式: 共有293条查询结果,搜索用时 15 毫秒
1.
Kristel Van Steen Nadia Tahri Geert Molenberghs 《Biometrical journal. Biometrische Zeitschrift》2004,46(2):187-202
Until recently, the most common parametric approaches to study the combined effects of several genetic polymorphisms located within a gene or in a small genomic region are, at the genotype level, logistic regressions and at the haplotype level, haplotype analyses. An alternative modeling approach, based on the case/control principle, is to regard exposures (e.g., genetic data such as derived from Single Nucleotide Polymorphisms – SNPs) as random and disease status as fixed and to use a marginal multivariate model that accounts for inter‐relationships between exposures. One such model is the multivariate Dale model. This model is based on multiple logistic regressions. That is why the model, applied in a case/control setting, leads to straightforward interpretations that are similar to those drawn in a classical logistic modeling framework. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
2.
Almond plants (Amygdalus communis L.) of the Garrigues variety were grown in the field drip irrigated and rainfed. Leaf water potential (Ψ) and leaf conductance
(g1) were determined throughout one growing season. Pre-dawn measurement for Ψ in the irrigated treatment was consistent through
the growing season, whereas in the rainfed treatment it decreased gradually. Ψ values at midday (Ψ minimum) was closely dependent
on atmospheric evaporative demand, and their recovery was quicker in the wet treatment than in the dry. The g1 values were higher in the wet than dry treatments, decreasing in both cases by leaf ageing. Maximum values for g1 were reached when evaporative demand was highest in the day. The relationship between Ψ and g1 revealed a decrease in the hysteresis throughout the growing season, being most marked in the dry treatment. The results
highlight the close dependence of Ψ and g1 on evaporative demand, leaf ageing and irrigtion treatment during the growing season. 相似文献
3.
Ding W. Wu John G. Duman Chi-Hing C. Cheng Francis J. Castellino 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1991,161(3):271-278
Summary Four antifreeze proteins (AFPs) were purified from larvae of the beetle Dendroides canadensis. The AFPs are similar in amino acid compositions, having high contents of hydrophilic amino acids (45–55 mol%) and cysteine (16 mol% Cys). Approximately half of the Cys residues form disulfide bridges, and both the disulfide bridges and free sulfhydryls are essential for activity. The N-terminals of the AFPs are blocked. The pH optimum of the AFPs is 7.8, but major loss of activity occurred only at very high pH (12.0). The detergents SDS and Triton X-100 did not inactivate the AFPs. Circular dichroism spectra indicate the presence of both and secondary structures in the AFPs, in addition to a large random structure component.Abbreviations
AFP
antifreeze protein
-
CD
circular dichroism
-
DTT
dithiothreitol
-
HPLC
high pressure liquid chromatography
-
PAGE
polyacrylamide gel electrophoresis
-
PAS
periodic acid Schiff
-
SDS
sodium dodecyl sulfate
-
TFA
trifluoroacetic acid 相似文献
4.
Ding Wen Wu John G. Duman 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1991,161(3):279-283
Summary Purified antifreeze proteins (AFPs) from the larvae of the beetle Dendroides canadensis do not produce the high levels of antifreeze activity seen in the hemolymph of overwintering larvae, even when the purified AFPs are assayed at very high concentrations. However, addition of certain proteins or agar (at concentrations sufficiently low that the gel state does not result) to the Dendroides AFP resulted in a 2–3-fold increase in activity. A 70-kDa protein with AFP-activating capabilities was purified from Dendroides larvae. Addition of this endogenous activator protein to a 4 mg·ml-1 solution of AFP increased the activity of the AFPs to values comparable to those of the hemolymph of overwintering larvae. Data derived from a modified immunoblot technique demonstrate that the activators bind to the AFP, or vice versa. Formation of this association must allow the AFP to block ice crystal growth by binding to the surface of potential seed crystals in the normal fashion. However, because the AFP-activator complex is much larger than the AFP alone, the complex probably blocks a greater surface area of the crystal and is thus a more efficient antifreeze.Abbreviations
AFP
antifreeze protein
-
BSA
bovine serum albumine
-
DEAE
diethylaminoethyl
-
Ig
immunoglubolin
-
LPIN
lipoprotein ice nucleator
-
PIN
protein ice nucleator
-
SDS
sodium dodecyl sulfate
-
PAGE
polyacrylamide gel electrophoresis
-
TH
thermal hysteresis 相似文献
5.
冷冻液温和季节对鼠尾过冷点的影响 总被引:3,自引:0,他引:3
为研究动物对寒冷的适应性,将鼠尾置于冷液浸冻,发现在一定条件下鼠尾组织可发生过冷现象。实验表明,鼠尾组织的过冷点和冷冻液温有关,同一季节冷冻液温越低过冷点越高;而不同季节相同冷冻条件下,冬季鼠尾组织的过冷点明显低于春季。 动物肢体组织的过冷特性是动物的抗寒冷特性,它和组织自身的物理化学性质有关。理沦证明,过冷度(△T)和表面张力(O)、摩尔质量(M),冰点(Ti)、密度(p)、摩尔凝固热(△H)及冰胚临界半径(rk)有关,其关系式为△T=26MTi/p△Hrk. 相似文献
6.
Cathrine Lillo Lucy H. Smith Hugh G. Nimmo Malcolm B. Wilkins 《Physiologia plantarum》1996,98(1):140-146
Nitrate reductase (NR, EC 1.6.6.1) was tested in crude extracts of leaves from Bryophyllum fedtschenkoi plants growing under alternating light/darkness as well as in excised leaves kept in continuous light or darkness. In most extracts NR activity was inhibited 20–80% by 5 m M Mg2+ A light or darkness shift (30 min darkness) during the first part of the photoperiod gave an increase in the Mg2+ inhibition and a decrease in NR activity. Magnesium ion inhibition of NR also showed diurnal variations. Strongest inhibition was found in extracts made during the latter part of the photoperiod and start of the dark period. Pre-incubation of crude extracts with ATP increased Mg2+ inhibition, indicating that phosphorylation of NR is involved in regulation of NR in Crassulacean acid metabolism (CAM) plants. In continuous light an increase in Mg2+ inhibition occurred after 20 h and 40 h, indicating a rhythm in the phosphorylation of NR. A delay in the production of nitrite in the assay (hysteresis) was generally seen in extracts susceptible to Mg2+ inhibition. The rhythms related to NR activity showed the same period length (20 h) as the rhythm in CO2 exchange. However, in contrast to the rhythm in CO2 exchange, NR rhythms were strongly damped in continuous light. In constant darkness the rhythms were even more damped. The results show that post-translational modification of CAM NR is influenced by light/darkness and by an endogenous rhythm. 相似文献
7.
Gernot Falkner Ferdinand Wagner John Victor Small Renate Falkner 《Journal of phycology》1995,31(5):745-753
The blue-green alga Anacystis nidulans Drouet (Synechococcus leopoliensis Raciborski) cultivated under phosphate-limited conditions adopts a threshold value in the nanomolar range below which uptake ceases. In this study, we investigated the influence of phosphate pulses on the regulation of uptake behavior during reestablishment of the threshold value. Short-term pulses had only a slight effect on uptake kinetics and, hence, on the threshold value, even if the population had been exposed several times to elevated concentrations above the steady-state level in the growth medium. The threshold value was also practically insensitive to the amount of phosphate stored during these short-term fluctuations. Long-term phosphate pulses resulted in a transition to a metastable state that was characterized by a severalfold higher threshold value. This transition, apparently an adaptation to the transiently elevated phosphate concentrations, was further studied by following the influx of 32 P-phosphate at constant external concentrations and was shown to be complete after a period of 10–20 min. After adaptation to pulses, the uptake behavior followed a linear flow-force relation over a wide range of external concentrations. This behavior was explained by the simultaneous operation of at least two uptake systems with different, but coordinated kinetic parameters. This linear flow-force relation facilitated a direct determination of the threshold value from uptake measurements. For applicability in the field the force-flow relation can be a diagnostic tool to assay for fluctuating phosphate and to establish threshold values below the normal measurable range . 相似文献
8.
Calcium in fungi 总被引:2,自引:0,他引:2
Abstract. Recently much experimental evidence has accumulated concerning intracellular calcium and its fundamental role as a regulator in eukaryotic cells. The literature relating to Ca2+ in fungi is large and diverse and this paper draws together the available information and discusses the particular functions of the ion in this group of organisms.
Uptake mechanisms in fungi are considered with special reference to the effect of Ca2+ on permeability and the systems responsible for transport of ions, sugars and amino acids. Discussion of the subcellular locations and distribution of Ca2+ is accompanied by a critique of methodology used in determination of subcellular sites of Ca2+ in fungi. The role of Ca2+ in morphogenesis in fungi is considered with particular reference to selected groups. 相似文献
Uptake mechanisms in fungi are considered with special reference to the effect of Ca
9.
The uptake of various amino acids into Streptomyces hydrogenans grown in chemostatically and turbidostatically controlled steady state cultures has been investigated. A close correlation between transport capacity and the growth rates of the cells was found. As shown by kinetic analysis, the increased transport is due to elevated maximum uptake rates, the apparent Michaelis constants remaining unchanged. Analysis of the unidirectional fluxes of cycloleucine revealed that not only the influx is raised as the growth rate is increased but also the efflux. Hence, the conclusion is drawn that the growth-rate dependent modulation of transport capacity is, at least, partially due to the variation of the concentration of active transport components. Since the cells were grown in the absence of external amino acids the results suggest that amino acid transport into S. hydrogenans is under the control of endogenous effectors.List of Abbreviations AIB
2-aminoisobutyric acid
- Cycloleucine
1-aminocyclopentane-1-carboxylic acid 相似文献
10.
Shuang Liu Yanjun Guan Yusong Sheng Yue Hu Yaoguang Rong Anyi Mei Hongwei Han 《Liver Transplantation》2020,10(13)
Additives are widely adopted for efficient, stable, and hysteresis‐free perovskite solar cells and play an important role in various breakthroughs of perovskite solar cells (PSCs). Herein the various additives adopted for PSCs are reviewed and their functioning mechanism and influence on device performance is described. The main roles of additives, modulating morphology of perovskite films, stabilizing phase of formamidinium (FA) and cesium (Cs)‐based perovskites, adjusting energy level alignment in PSCs, suppressing nonradiative recombination in perovskites, eliminating hysteresis, enhancing operational stability of PSCs, are summarized. 相似文献