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1.
Charge is a fundamental property of macromolecules in solution. However, estimation of the apparent charge on polyions has confounded science for decades. Presented here is a general method to determine directly the apparent charge on a polyion, regardless of its size or shape. This new method uses equilibrium electrophoresis, a procedure in which opposing solute flows from electrophoresis and from diffusion balance everywhere as the system reaches a steady-state distribution. The method uses only small quantities of materials, is nondestructive, and requires only simple, inexpensive instrumentation. Here we describe a prototype apparatus, demonstrate the phenomenon, and present experimental examples of the procedure. 相似文献
2.
Three allosteric states are required to describe the relaxation of (carbon monoxy) hemoglobin following flash photolysis. Combined absorbance and fluorescence probes were used. The absorbance signals consist of a component corresponding to ligand recombination and a component for the R-T transition. The fluorescence of 8-hydroxy-1,3,6-pyrenetrisulfonate (HPT), an analogue of 2,3-diphosphoglycerate, shows rates and amplitudes correlated with the absorbance transients. Measurements were made at pII 6, 6.5, and 7.0 at CO partial pressures of 0.1 and 1 atm. The fractional photolysis was varied in each case to change the initial distribution of the R states. Data show an immediate absorbance change due to ligand dissociation, while the changes in the ligand isosbestic and the fluorescence signals occur with time constants of 80 microseconds (at pH 6.5). The signals then show a biphasic return to equilibrium, characteristic of the allosteric system. The measurements provide three independent probes of the kinetics of the substates of hemoglobin. Although the ligand binding data can be generally represented by a two-state model, the fluorescence data require T states with different affinities for HPT. 相似文献
3.
The IgE-mediated histamine release from mouse mast cells requires Ca++, is optimal at 37 degrees C, and is enhanced by phosphatidylserine. The rate of release is relatively slow. The mast cells can be activated to release histamine by either anti-IgE or anti-Fab antibodies and, in the case of cells from sensitized mice, by the immunizing antigen. The incubation of mast cells with antigen in the absence of Ca++ or phosphatidylserine fails to release histamine. Such cells are desensitized to the further addition under optimal conditions of the same antigen. Desensitization is antigen specific, requires optimal levels of antigen, and occurs at both 30 degrees and 37 degrees C. In contrast, anti-IgE desensitizes all IgE-mediated histamine release reactions. 相似文献
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5.
Salicylic acid is an important signalling molecule involved in both locally and systemically induced disease resistance responses. Recent advances in our understanding of plant defence signalling have revealed that plants employ a network of signal transduction pathways, some of which are independent of salicylic acid. Evidence is emerging that jasmonic acid and ethylene play key roles in these salicylic acid-independent pathways. Cross-talk between the salicylic acid-dependent and the salicylic acid-independent pathways provides great regulatory potential for activating multiple resistance mechanisms in varying combinations. 相似文献
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7.
Two main mechanisms are thought to affect the prevalence of endophyte-grass symbiosis in host populations: the mode of endophyte transmission, and the fitness differential between symbiotic and non-symbiotic plants. These mechanisms have mostly been studied in synthetic grass populations. If we are to improve our understanding of the ecological and evolutionary dynamics of such symbioses, we now need to determine the combinations of mechanisms actually operating in the wild, in populations shaped by evolutionary history. We used a demographic population modeling approach to identify the mechanisms operating in a natural stand of an intermediate population (i.e. 50% of plants symbiotic) of the native grass Festuca eskia. We recorded demographic data in the wild over a period of three years, with manipulation of the soil resources for half the population. We developed two stage-structured matrix population models. The first model concerned either symbiotic or non-symbiotic plants. The second model included both symbiotic and non-symbiotic plants and took endophyte transmission rates into account. According to our models, symbiotic had a significantly higher population growth rate than non-symbiotic plants, and endophyte prevalence was about 58%. Endophyte transmission rates were about 0.67 or 0.87, depending on the growth stage considered. In the presence of nutrient supplementation, population growth rates were still significantly higher for symbiotic than for non-symbiotic plants, but endophyte prevalence fell to 0%. At vertical transmission rates below 0.10–0.20, no symbiosis was observed. Our models showed that a positive benefit of the endophyte and vertical transmission rates of about 0.6 could lead to the coexistence of symbiotic and non-symbiotic F. eskia plants. The positive effect of the symbiont on host is not systematically associated with high transmission rates of the symbiont over short time scales, in particular following an environmental change. 相似文献
8.
Chintamani Pranjal Kulshreshtha Anurupa Chakraborty LC Singh Ashwani K Mishra Dinesh Bhatnagar Sunita Saxena 《World journal of surgical oncology》2010,8(1):1-9
Voltage gated potassium channels have been extensively studied in relation to cancer. In this review, we will focus on the role of two potassium channels, Ether à-go-go (Eag), Human ether à-go-go related gene (HERG), in cancer and their potential therapeutic utility in the treatment of cancer. Eag and HERG are expressed in cancers of various organs and have been implicated in cell cycle progression and proliferation of cancer cells. Inhibition of these channels has been shown to reduce proliferation both in vitro and vivo studies identifying potassium channel modulators as putative inhibitors of tumour progression. Eag channels in view of their restricted expression in normal tissue may emerge as novel tumour biomarkers. 相似文献
9.
AB Chang NC Cox J Purcell JM Marchant PJ Lewindon GJ Cleghorn LC Ee GD Withers MK Patrick J Faoagali 《Respiratory research》2005,6(1):1-5
Background and methods
Human metapneumovirus (hMPV) is a recently discovered respiratory virus associated with bronchiolitis, pneumonia, croup and exacerbations of asthma. Since respiratory viruses are frequently detected in patients with acute exacerbations of COPD (AE-COPD) it was our aim to investigate the frequency of hMPV detection in a prospective cohort of hospitalized patients with AE-COPD compared to patients with stable COPD and to smokers without by means of quantitative real-time RT-PCR.Results
We analysed nasal lavage and induced sputum of 130 patients with AE-COPD, 65 patients with stable COPD and 34 smokers without COPD. HMPV was detected in 3/130 (2.3%) AE-COPD patients with a mean of 6.5 × 105 viral copies/ml in nasal lavage and 1.88 × 105 viral copies/ml in induced sputum. It was not found in patients with stable COPD or smokers without COPD.Conclusion
HMPV is only found in a very small number of patients with AE-COPD. However it should be considered as a further possible viral trigger of AE-COPD because asymptomatic carriage is unlikely. 相似文献10.
Hitoshi?YoshidaEmail author Masayasu?Nagata Koji?Saito Kevin?LC?Wang Joseph?R?Ecker 《BMC plant biology》2005,5(1):14