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61.
The mannose transporter of bacterial phosphoenolpyruvate:sugar phosphotransferase system (PTS) mediates uptake of mannose, glucose, and related hexoses by a mechanism that couples translocation with phosphorylation of the substrate. It consists of the transmembrane IICMan.IIDMan complex and the cytoplasmic IIABMan subunit. IIABMan has two domains (IIA and IIB) that are linked by a 60-A long alanine-proline-rich linker. IIABMan transfers phosphoryl groups from the phospho-histidine-containing phospho-carrier protein of the PTS to His-10 on IIA, hence to His-175 on IIB, and finally to the 6'-OH of the transported hexose. IIABMan occurs as a stable homodimer. The subunit contact is mediated by a swap of beta-strands and an extensive contact area between the IIA domains. The H10C and H175C single and the H10C/H175C double mutants were used to characterize the phosphoryl transfer between IIA to IIB. Subunits do not exchange between dimers under physiological conditions, but slow phosphoryl transfer can take place between subunits from different dimers. Heterodimers of different subunits were produced in vitro by GuHCl-induced unfolding and refolding of mixtures of two different homodimers. With respect to wild-type homodimers, the heterodimers have the following activities: wild-type.H10C, 50%; wild-type.H175C 45%; H10C.H175C, 37%; and wild-type.H10C/H175C (double mutant), 29%. Taken together, this indicates that both cis and trans pathways contribute to the maximal phosphotransferase activity of IIABMan. A phosphoryl group on a IIA domain can be transferred either to the IIB domain on the same or on the second subunit in the dimer, and interruption of one of the two pathways results in a reduction of the activity to 70-80% of the control. 相似文献
62.
63.
Soil microorganisms mediate many processes such as nitrification, denitrification, and methanogenesis that regulate ecosystem functioning and also feed back to influence atmospheric chemistry. These processes are of particular interest in freshwater wetland ecosystems where nutrient cycling is highly responsive to fluctuating hydrology and nutrients and soil gas releases may be sensitive to climate warming. In this review we briefly summarize research from process and taxonomic approaches to the study of wetland biogeochemistry and microbial ecology, and highlight areas where further research is needed to increase our mechanistic understanding of wetland system functioning. Research in wetland biogeochemistry has most often been focused on processes (e.g., methanogenesis), and less often on microbial communities or on populations of specific microorganisms of interest. Research on process has focused on controls over, and rates of, denitrification, methanogenesis, and methanotrophy. There has been some work on sulfate and iron transformations and wetland enzyme activities. Work to date indicates an important process level role for hydrology and soil nutrient status. The impact of plant species composition on processes is potentially critical, but is as yet poorly understood. Research on microbial communities in wetland soils has primarily focused on bacteria responsible for methanogenesis, denitrification, and sulfate reduction. There has been less work on taxonomic groups such as those responsible for nitrogen fixation, or aerobic processes such as nitrification. Work on general community composition and on wetland mycorrhizal fungi is particularly sparse. The general goal of microbial research has been to understand how microbial groups respond to the environment. There has been relatively little work done on the interactions among environmental controls over process rates, environmental constraints on microbial activities and community composition, and changes in processes at the ecosystem level. Finding ways to link process-based and biochemical or gene-based assays is becoming increasingly important as we seek a mechanistic understanding of the response of wetland ecosystems to current and future anthropogenic perturbations. We discuss the potential of new approaches, and highlight areas for further research. 相似文献
64.
Summary The relationship between the rate of Cl– transport and the electrical properties ofHalicystis parvula was investigated. Three metabolic inhibitors-darkness, cyanide (2mm), and low temperature (4°C)-all rapidly and reversibly reduce both the short circuit current (SCC), which is a measure of net Cl– transport, and the vacuole electrical potential (PD). Plotting thePD vs. SCC for inhibited cells yields a linear regression with ay-intercept of zero. ThePD is also greatly reduced when the [Cl–] of the external medium is lowered. Raising the external [K+] produces an appreciable, but less than Nernstian, depolarization, while increasing the external [H+] tenfold has no net effect on thePD. Decreasing the external [Na+] by tenfold produces only a slight depolarization. Thus, the outer plasma membrane appears to be moderately selective for K+ over Na+ or H+. The effects of ion substitutions in the vacuolar perfusing solutions on thePD reveal that the vacuolar membrane does not discriminate electrically between Cl– and the much larger anions, isethionate and benzenesulfonate, or between Na+ and K+. The data suggest that in internally perfused cells ofH. parvula generation of thePD of –50 to –60 mV by a transport system involving only electroneutral pumps is unlikely and that most of thisPD is generated by an electrogenic Cl– pump. 相似文献
65.
Jessica L. M. Gutknecht Christopher B. Field Teri C. Balser 《Global Change Biology》2012,18(7):2256-2269
We used microbial lipid analysis to analyze microbial biomass and community structure during 6 years of experimental treatment at the Jasper Ridge Global Change Experiment (JRGCE), a long‐term multi‐factor global change experiment in a California annual grassland. The microbial community fingerprint and specific biomarkers varied substantially from year to year, in both control and experimental treatment plots. Possible drivers of the variability included plant growth, soil moisture, and ambient temperature. Surprisingly, background variation in the microbial community was of a larger magnitude than even very significant treatment effects, and this variation appeared to constrain responses to treatment. Microbial communities were mostly not responsive or not consistently responsive to the experimental treatments. Both arbuscular mycorrhizal fungi biomarker abundance (16 : 1 ω5c) and the fungal to bacterial ratio were lower under nitrogen addition in most years. Bacterial lipid biomarker abundances (15 : 0 iso and 16 : 1 ω7c) were higher under nitrogen addition in 2002, the year of largest microbial biomass, suggesting that bacteria could respond more to nitrogen addition in years of better growth conditions. Nitrogen addition and warming led to an interactive effect on the Gram‐positive bacterial biomarker and the fungal to bacterial ratio. These patterns indicate that in California grassland ecosystems, microbial communities may not respond substantially to future changes in climate and that nitrogen deposition may be a determinant of the soil response to global change. Further, year‐to‐year variation in microbial growth or community composition may be important determinants of ecosystem response to global change. 相似文献
66.
Anna Małkiewicz Maria Skrzypkowska Bartosz Słomiński Janusz Siebert Piotr Gutknecht Jolanta Myśliwska 《Molecular biology reports》2016,43(9):967-975
Our purpose was to determine whether the VEGF ?152 G/A polymorphism could be associated with chronic kidney disease and endothelial dysfunction in hypertensive patients. There were 100 healthy volunteers enrolled into the control group. The group of patients was constituted by 99 consecutively admitted hypertensive patients referred to our Institution by their general practitioner. All patients were treated with anti-hypertensive polytherapy. Presented study revealed that the hypertensive patients bearing the GG genotype were characterized by the highest values of diastolic blood pressure and markers of endothelial damage such as Angiogenin, Endostatin, CRP as well as von Willebrandt factor. In addition, higher number of immature endothelial progenitor cells with CD34+CD133+, CD34+CD133- markers was observed in GG hypertensive carriers while in normotensive individuals no differences were found. Such phenomenon may indicate an increased mobilization of bone-marrow derived endothelial progenitors. It may testify to the preserved compensatory mechanism in chronic kidney disease (CKD) patients until the G3a stage of the disease. Moreover, patients with higher estimated glomerular filtration rate (eGFR) level had lower of vWf and Endostatin values, and higher level of VEGF. Taken together our findings clearly indicate the ?152 GG hypertensive carriers as more prone to develop CKD. We can suspect that the VEGF ?152 GG genotype is strongly associated with hypertension-dependent CKD. 相似文献
67.
Jonas Waider Florian Proft Georg Langlhofer Esther Asan Klaus-Peter Lesch Lise Gutknecht 《Histochemistry and cell biology》2013,139(2):267-281
While tryptophan hydroxylase-2 (Tph2) null mutant (Tph2 ?/?) mice are completely deficient in brain serotonin (5-HT) synthesis, the formation of serotonergic neurons and pathfinding of their projections are not impaired. However, 5-HT deficiency, during development and in the adult, might affect morphological and functional parameters of other neural systems. To assess the influence of 5-HT deficiency on γ-amino butyric acid (GABA) systems, we carried out measurements of GABA concentrations in limbic brain regions of adult male wildtype (wt), heterozygous (Tph2 +/?) and Tph2 ?/? mice. In addition, unbiased stereological estimation of GABAergic interneuron numbers and density was performed in subregions of amygdala and hippocampus. Amygdala and prefrontal cortex displayed significantly increased and decreased GABA concentrations, respectively, exclusively in Tph2 +/? mice while no changes were detected between Tph2 ?/? and wt mice. In contrast, in the hippocampus, increased GABA concentrations were found in Tph2 ?/? mice. While total cell density in the anterior basolateral amygdala did not differ between genotypes, the number and density of the GABAergic interneurons were significantly decreased in Tph2 ?/? mice, with the group of parvalbumin (PV)-immunoreactive (ir) interneurons contributing somewhat less to the decrease than that of non-PV-ir GABAergic interneurons. Major morphological changes were also absent in the dorsal hippocampus, and only a trend toward reduced density of PV-ir cells was observed in the CA3 region of Tph2 ?/? mice. Our findings are the first to document that life-long reduction or complete lack of brain 5-HT transmission causes differential changes of GABA systems in limbic regions which are key players in emotional learning and memory processes. The changes likely reflect a combination of developmental alterations and functional adaptations of emotion circuits to balance the lack of 5-HT, and may underlie altered emotional behavior in 5-HT-deficient mice. Taken together, our findings provide further insight into the mechanisms how life-long 5-HT deficiency impacts the pathogenesis of anxiety- and fear-related disorders. 相似文献
68.
Diffusion of histamine, theophylline and tryptamine through planar lipid bilayer membranes was studied as a function of pH. Membranes were made of egg phosphatidylcholine plus cholesterol (1 : 1 mol ratio) in tetradecane. Tracer fluxes and electrical conductances were used to estimate the permeabilities to nonionic and ionic species. Only the nonionic forms crossed the membrane at a significant rate. The membrane permeabilities to the nonionic species were: histamine, ; theophylline, ; and tryptamine, . Chemical reactions in the unstirred layers are important in the transport of tryptamine and theophylline, but not histamine. For example, as pH decreased from 10.0 to 7.5 the ratio of nonionic (B) to ionic (BH+) tryptamine decreased by 300-fold, but the total tryptamine permeability decreased only 3-fold. The relative insensitivity of the total tryptamine permeability to the ratio, [B]/[BH+], is due to the rapid interconversion of B and BH+ in the instirred layers. Our model describing diffusion and reaction in the unstirred layers can explain some ‘anomalous’ relationships between pH and weak acid/base transport through lipid bilayer and biological membranes. 相似文献
69.
John Gutknecht 《Journal of bioenergetics and biomembranes》1987,19(5):427-442
The proton/hydroxide (H+/OH–) permeability of phospholipid bilayer membranes at neutral pH is at least five orders of magnitude higher than the alkali or halide ion permeability, but the mechanism(s) of H+/OH– transport are unknown. This review describes the characteristics of H+/OH– permeability and conductance through several types of planar phospholipid bilayer membranes. At pH7, the H+/OH– conductances (G
H/OH) range from 2–6 nS cm–2, corresponding to net H+/OH– permeabilities of (0.4–1.7)×10–5 cm sec–1. Inhibitors ofG
H/OH include serum albumin, phloretin, glycerol, and low pH. Enhancers ofG
H/OH include chlorodecane, fatty acids, gramicidin, and voltages >80 mV. Water permeability andG
H/OH are not correlated. The characteristics ofG
H/OH in fatty acid (weak acid) containing membranes are qualitatively similar to the controls in at least eight different respects. The characteristics ofG
H/OH in gramicidin (water wire) containing membranes are qualitatively different from the controls in at least four different respects. Thus, the simplest explanation for the data is thatG
H/OH in unmodified bilayers is due primarily to weakly acidic contaminants which act as proton carriers at physiological pH. However, at low pH or in the presence of inhibitors, a residualG
H/OH remains which may be due to water wires, hydrated defects, or other mechanisms. 相似文献
70.