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991.
BassiriRad Hormoz Prior Stephen A. Norby Rich J. Rogers Hugo H. 《Plant and Soil》1999,217(1-2):195-204
Models describing plant and ecosystem N cycles require an accurate assessment of root physiological uptake capacity for NH
4
+
and NO
3
-
under field conditions. Traditionally, rates of ion uptake in field-grown plants are determined by using excised root segments
incubated for a short period in an assay solution containing N either as a radioactive or stable isotope tracer (e.g., 36ClO3 as a NH
4
+
analogue, 14CH3NH3 as an NO
3
-
analogue or 15NH
4
+
and 15NO
3
-
). Although reliable, this method has several drawbacks. For example, in addition to radioactive safety issues, purchase and
analysis of radioactive and stable isotopes is relatively expensive and can be a major limitation. More importantly, because
excision effectively interrupts exchange of compounds between root and shoot (e.g., carbohydrate supply to root and N transport
to shoot), the assay must be conducted quickly to avoid such complications. Here we present a novel field method for simultaneous
measurements of NH
4
+
and NO
3
-
uptake kinetics in intact root systems. The application of this method is demonstrated using two tree species; red maple
(Acer rubrum) and sugar maple (Acer saccharum) and two crop species soybean (Glycine max) and sorghum (Sorghum bicolor). Plants
were grown in open-top chambers at either ambient or elevated levels of atmospheric CO2 at two separate US national sites involved in CO2 research. Absolute values of net uptake rates and the kinetic parameters determined by our method were found to be in agreement
with the literature reports. Roots of the crop species exhibited a greater uptake capacity for both N forms relative to tree
species. Elevated CO2 did not significantly affect kinetics of N uptake in species tested except in red maple where it increased root uptake capacity,
V, for NH
4
+
. The application, reliability, advantages and disadvantages of the method are discussed in detail.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
992.
Much recent progress has been made to understand the impact of proteome allocation on bacterial growth; much less is known about the relationship between the abundances of the enzymes and their substrates, which jointly determine metabolic fluxes. Here, we report a correlation between the concentrations of enzymes and their substrates in Escherichia coli. We suggest this relationship to be a consequence of optimal resource allocation, subject to an overall constraint on the biomass density: For a cellular reaction network composed of effectively irreversible reactions, maximal reaction flux is achieved when the dry mass allocated to each substrate is equal to the dry mass of the unsaturated (or “free”) enzymes waiting to consume it. Calculations based on this optimality principle successfully predict the quantitative relationship between the observed enzyme and metabolite abundances, parameterized only by molecular masses and enzyme–substrate dissociation constants (Km). The corresponding organizing principle provides a fundamental rationale for cellular investment into different types of molecules, which may aid in the design of more efficient synthetic cellular systems.This study shows that in E. coli, the cellular mass of each metabolite approximately equals the combined mass of the free enzymes waiting to consume it; this simple relationship arises from the optimal utilization of cellular dry mass, and quantitatively describes available experimental data. 相似文献
993.
Editorial: Software survey section 相似文献
994.
Editorial: Software survey section 相似文献
995.
Mariela Bollini Juan José Casal Diego E. Alvarez Lucía Boiani Mercedes González Hugo Cerecetto Ana María Bruno 《Bioorganic & medicinal chemistry》2009,17(4):1437-1444
A series of novel benzoimidazo and N-aryl-5-oxo-imidazo[1,2-b]isoquinoline-10-carbothioamides was developed. All the compounds were evaluated for their in vitro action against the epimastigote form of Trypanosoma cruzi. Four of them showed higher activity than Nifurtimox. Their unspecific cytotoxicity was evaluated using HeLa and L6 cells, being non-toxic at concentrations at least 15 and 200 times higher than that of T. cruzi IC50. To gain insight into the mechanism of action, their DNA binding properties and reactivity with glutathione were studied, and QSAR study was performed. 相似文献
996.
Kristina M. Orrling Melissa R. Marzahn Hugo Gutiérrez-de-Terán Johan Åqvist Ben M. Dunn Mats Larhed 《Bioorganic & medicinal chemistry》2009,17(16):5933-5949
The impact of moving the P1 side-chain from the β-position to the α-position in norstatine-containing plasmepsin inhibitors was investigated, generating two new classes of tertiary alcohol-comprising α-benzylnorstatines and α-phenylnorstatines. Twelve α-substituted norstatines were designed, synthesized and evaluated for their inhibitory potencies against plasmepsin II and the plasmepsin IV orthologues (PM4) present in the digestive vacuole of all four Plasmodium species causing malaria in man. New synthetic routes were developed for producing the desired α-substituted norstatines as pure stereoisomers. The best compounds provided Ki values in the nanomolar range for all PM4, with a best value of 110 nM in PM4 from Plasmodium ovale. In addition, excellent selectivity over the closely related human aspartic protease Cathepsin D was achieved. The loss of affinity to Plasmodium falciparum PM4, which was experienced upon the move of the P1 substituent, was rationalized by the calculation of inhibitor–protein binding affinities using the linear interaction energy method (LIE). 相似文献
997.
Fernando Rodrigues da Silva Mário Almeida‐Neto Vitor Hugo Mendonça do Prado Célio Fernando Baptista Haddad Denise de Cerqueira Rossa‐Feres 《Journal of Biogeography》2012,39(9):1720-1732
Aim The diversity of reproductive modes among amphibians constitutes a striking example of how differences in the biology of species provide important explanations for species distribution patterns on a broad scale. We hypothesize that sites with a higher humidity level will support more modes of reproduction than drier sites and will consequently exhibit a higher phylogenetic diversity. Furthermore, if there is a gradient in the tolerance of reproductive modes to desiccation, there will be a nested pattern in the composition of reproductive modes among sites. Location Twenty‐seven forest sites in the Brazilian Atlantic Forest. Methods Through a path analysis approach, we evaluated the direct and indirect effects of the humidity level on the number of reproductive modes, as well as the relative importance of both variables on amphibian phylogenetic diversity. A nestedness analysis was used to quantify the extent to which the compositions of both species and reproductive modes in drier sites correspond to subsets of those in sites with higher annual precipitation. Results We found that the reproductive modes present in drier sites are non‐random subsets of those present in sites with higher humidity levels. Because reproductive modes are phylogenetically conserved among amphibians, sites with a greater number of reproductive modes supported greater phylogenetic diversity. Sites with high precipitation throughout the year provided suitable environmental conditions for a larger number of reproductive modes, whereas sites with low precipitation and typical seasonal climates supported only those reproductive modes specialized to resist desiccation. Main conclusions Our results show that humidity‐related variables are key environmental factors related to both the richness of reproductive modes and phylogenetic diversity. Our results support the hypothesis that the higher phylogenetic diversity found in moister sites reflects differences in the tolerance to desiccation among different reproductive modes. Given that reproductive modes are associated with susceptibility to desiccation, their incorporation into explanatory models may trigger a significant advance in the understanding of the mechanisms regulating the species richness and composition of amphibian communities. 相似文献
998.
Claudia Seyler Patrick A. SchweizerEdgar Zitron Hugo A. KatusDierk Thomas 《Biochemical and biophysical research communications》2014
Atrial fibrillation (AF) contributes significantly to cardiovascular morbidity and mortality. The growing epidemic is associated with cardiac repolarization abnormalities and requires the development of more effective antiarrhythmic strategies. Two-pore-domain K+ channels stabilize the resting membrane potential and repolarize action potentials. Recently discovered K2P17.1 channels are expressed in human atrium and represent potential targets for AF therapy. However, cardiac electropharmacology of K2P17.1 channels remains to be investigated. This study was designed to elucidate human K2P17.1 regulation by antiarrhythmic drugs. 相似文献
999.
This study aimed to quantify the time-motion demands and intra-team movement synchronization during the pre-season matches of a professional soccer team according to the opposition level. Positional data from 20 players were captured during the first half of six pre-season matches of a Portuguese first league team. Time-motion demands were measured by the total distance covered and distance covered at different speed categories. Intra-team coordination was measured by calculating the relative phase of all pairs of outfield players. Afterwards, the percentage of time spent in the −30° to 30° bin (near-in-phase mode of coordination) was calculated for each dyad as a measure of space-time movement synchronization. Movement synchronization data were analyzed for the whole team, according to each dyad average speed and by groups of similar dyadic synchronization tendencies. Then, these data were compared according to the opponent team level (first league; second league; amateurs). Time-motion demands showed no differences in total distance covered per opposition levels, while matches opposing teams of superior level revealed more distance covered at very high intensity. Competing against superior level teams implied more time in synchronized behavior for the overall displacements and displacements at higher intensities. These findings suggest that playing against higher-level opponents (1st league teams) increased time-motion demands at high intensities in tandem with intra-team movement synchronization tendencies. 相似文献
1000.
Homologous recombination makes use of sequence homology to repair DNA and to rearrange genetic material. In mammals, these processes have mainly been characterized using cultured cell systems. We have developed an assay that allows us to quantitatively analyze homologous recombination in vivo in the mouse embryo. Transgenic mouse lines were generated by microinjection into a fertilized mouse ovum of a vector containing two homologous LINE-1 (L1) sequences arranged as a direct repeat: these sequences can recombine with each other and with endogenous L1 sequences before, during or after integration of the vector into the genome. Using a plasmid rescue procedure, we determined the composition of the integrated vector array in several transgenic mice and their descendants. Homologous recombination frequencies were found to be strikingly high, involving 70% of integrated vectors in some arrays, with homologous deletions being five times more frequent than gene conversion without crossing-over. Interestingly, non-homologous recombination was found to be much less frequent. We also found that endogenous L1 sequences could be involved in homologous recombination events in the mouse embryo, and that the integrated arrays could be modified from generation to generation by homologous recombination between the integrated L1 sequences. 相似文献