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991.
Variations in leaf nitrogen concentration (Nm), mass-to-area ratio (Ma), amount of leaf nitrogen per unit leaf area (Na), and non-structural carbohydrates were measured in well-lit girdled branches of 11-year-old mango trees that were experiencing similar conditions of irradiance and gap fraction. The influence of source–sink relationships was studied by testing three levels of leaf-to-fruit ratio: 40, 70 and 150, during the period of linear fruit growth. Na was negatively correlated to the leaf-to-fruit ratio. Differences in Na were reflected in differences in net photosynthetic assimilation, Anet, although they could not fully account for them. All differences in Na resulted exclusively from differences in Nm, not Ma. Starch and total non-structural carbohydrates accumulated in the leaves as the result of higher leaf-to-fruit ratio, which suggests that the leaf carbohydrate status may play a role in photosynthetic acclimation to fruit load in mango. These observations complement previous findings where photosynthetic acclimation to light was found to be driven by changes in Ma, while Nm remained almost constant over a large range of gap fractions. Observations about the effect of fruit load were also in contrast with previous observations, since no evidence was found that leaf carbohydrate status played any role in photosynthetic acclimation to light. This study demonstrates that acclimation to changing source–sink relationships does not follow the same pattern as acclimation to progressive shading; but these observations do suggest that there may be different mechanisms by which leaves acclimatise to changing conditions. 相似文献
992.
Radioactive leucine was injected into the portal vein of rats followed after 15 seconds by a 180 fold excess of nonradioactive leucine. An albumin-like protein in the liver became highly labelled within 15 minutes after injection. After 150 minutes, the radioactivity in the albumin-like protein had decreased to one tenth. In the serum, radioactively labelled albumin started to appear after 15 minutes and increased there-after up to 150 minutes after injection. Radioactivity in albumin within the liver remained constant at a low level. These results suggest that the albumin-like protein is a biological precursor protein of serum albumin, i.e. a proalbumin. 相似文献
993.
Nataša Obermajer Urban Švajger Sara Sattin Marko Anderluh 《Analytical biochemistry》2010,406(2):222-229
We report a new dendritic cell adhesion assay, using either immature or mature dendritic cells, for identifying functional dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN) inhibitors. Because immature dendritic cells are responsible for pathogen binding and invasion, this in vitro assay provides an important link between in vitro results and pathogen-based in vivo assays. Furthermore, this assay does not require laborious expression, refolding, and purification of DC-SIGN carbohydrate recognition domain or extracellular domain as receptor-based assays. The assay power evaluated with Z and Z′ parameters enables screening of compound libraries and determination of IC50 values in the first stage of DC-SIGN inhibitor development. 相似文献
994.
E. Bresso V. Leroux M. Urban K. E. Hammond-Kosack B. Maigret N. F. Martins 《Journal of molecular modeling》2016,22(7):163
Fusarium head blight (FHB) is one of the most destructive diseases of wheat and other cereals worldwide. During infection, the Fusarium fungi produce mycotoxins that represent a high risk to human and animal health. Developing small-molecule inhibitors to specifically reduce mycotoxin levels would be highly beneficial since current treatments unspecifically target the Fusarium pathogen. Culmorin possesses a well-known important synergistically virulence role among mycotoxins, and longiborneol synthase appears to be a key enzyme for its synthesis, thus making longiborneol synthase a particularly interesting target. This study aims to discover potent and less toxic agrochemicals against FHB. These compounds would hamper culmorin synthesis by inhibiting longiborneol synthase. In order to select starting molecules for further investigation, we have conducted a structure-based virtual screening investigation. A longiborneol synthase structural model is first built using homology modeling, followed by molecular dynamics simulations that provided the required input for a protein–ligand ensemble docking procedure. From this strategy, the three most interesting compounds (hits) were selected among the 25 top-ranked docked compounds from a library of 15,000 drug-like compounds. These putative inhibitors of longiborneol synthase provide a sound starting point for further studies involving molecular modeling coupled to biochemical experiments. This process could eventually lead to the development of novel approaches to reduce mycotoxin contamination in harvested grain. 相似文献
995.
Magdalena M. Wiedermann Urban Gunnarsson Mats B. Nilsson Annika Nordin Lars Ericson 《Oikos》2009,118(3):449-456
Oligotrophic, Sphagnum -dominated peatlands have been regarded as long-term stable ecosystems that function as carbon sinks. As a result of environmental perturbations, particularly anthropogenic N deposition, this view is now increasingly questioned. We examined whether small-scale field experiments can predict the direction and magnitude of ecosystem responses to increased N supply. We, therefore, compared data from a 10-year field experiment (involving deposition of 2, 15 and 30 kg N ha−1 year−1 ) with data from a gradient associated with increased N deposition (2, 8 and 12 kg N ha−1 year−1 ). We chose to compare: (1) the physiological response of Sphagnum balticum , measured in the form of N accumulation as free amino acids (NAA ); and (2) changes in the total Sphagnum cover, the cover of S. balticum , and vascular plant cover. In all cases we found a highly significant correlation between the two data sets. We attribute the high correspondence between the two data sets to the key function of the dominant group of organisms, the Sphagna, that monopolize N availability and control the water balance, creating an environment hostile to vascular plants. Thus the key role of Sphagna as ecosystem engineers seems to supersede the role of other, scale-dependent processes. We also conclude that NAA is a sensitive indicator that can be used to signal the slow and gradual shift from Sphagnum to vascular plant dominance. 相似文献
996.
997.
J L Urban M L Kripke H Schreiber 《Journal of immunology (Baltimore, Md. : 1950)》1986,137(9):3036-3041
Using tumor-specific effector cells as probes, we have studied the immunologic changes that occur in tumor cells during continuous growth in a host. As a model, we used a highly immunogenic ultraviolet light (UV)-induced tumor that is rejected regularly by normal mice but grows progressively when transplanted into UV-irradiated mice. The immunogenic tumor growing continuously in these partially immunocompromised mice gave rise to genetically stable progressor variants that were poorly immunogenic. A sequence of changes in susceptibility to activated macrophages and tumor-specific cytolytic T cells was observed when serial reisolates from the continuously growing tumors were analyzed. First, the tumor cells developed resistance to the cytocidal effects of activated macrophages. This was followed by the loss of one and then a second tumor-specific antigen defined by syngeneic cytolytic T cells. The phenotypes of the developing antigen loss variants and their sequence of appearance were the same in several independent experiments, and the process was apparently determined by a hierarchy of the host's immune response to multiple independent tumor-specific antigens expressed by a single malignant cell. Our ability to generate the predicted variants in vitro before they actually appear in vivo suggests a possible approach to preventing the outgrowth of such immunoselected variants from a tumor. 相似文献
998.
Despite a long history of observations of the hemiparasitic plant, mistletoe, the mechanism of mineral movement from the host to the mistletoe is still not fully understood. In this article, we focused on the leaf development and nutrient dynamics of Loranthus europaeus and the host tree, Quercus pubescens. The nitrogen, potassium and calcium contents of leaves, current-year twigs and 1-year-old twigs were analysed. The timing of the leaf development differed between species. Leaf expansion occurred in the first 23 and 136?days, and leaf senescence took 78 and 24?days for Quercus and Loranthus, respectively. The similar nitrogen concentrations per unit leaf area may indicate that both species have the same assimilation rate. The differences in nutrient accumulation seem to support the hypothesis that nitrogen is the limiting nutrient in the transpiration stream. Larger differences in the nutrient dynamics between species were revealed in the accumulation potassium and calcium. Nutrients seemed to be transferred passively through the xylem sap between Loranthus and Quercus as we found a strong correlation between the calcium and potassium concentrations within the species and between the species. There was no correlation in the case of 1-year-old twigs, possibly due to the relatively small amount of nutrients incorporated into 1-year-old twigs and the fact that nutrient translocation occurs according the needs of the physiologically more active leaves and current-year-old twigs. 相似文献
999.
Abstract An isolation procedure for the 20,000-dalton variant of human growth hormone has been devised to improve the yield of the final product. The improvement involved elimination of cumbersome steps that decreased yield, and modification of chromatography on DEAE-cellu-lose to provide better separation of the variant from the major form of growth hormone. We reported (1) an isolation procedure for the 20,000-dalton variant of human growth hormone (hGH20K) (2) which provided quite homogeneous material but the yields were not optimum. The initial steps were cumbersome and losses resulted from them. In addition, there was the problem that in order to completely remove the major 22,000-dalton form of the hormone (hGH) during the final chromatography step (DEAE-cellulose), only the leading edge of the hGH20k?peak could be used. The trailing part of the peak was always mixed with hGH and reworking this mixture resulted in losses. We have modified the procedure so that time-consuming steps were eliminated and the final chromatography step was improved so that now the hGH20K can be separated from hGH by a single column. 相似文献
1000.
Chemical evidence for the difference between albumins from microsomes and serum and a possible precursor-product relationship 总被引:2,自引:0,他引:2
J Urban A S Inglis K Edwards G Schreiber 《Biochemical and biophysical research communications》1974,61(2):494-501
Immunologically isolated albumin from rat liver microsomes separates on DEAE-cellulose into almost equal proportions of an albumin-like protein and authentic albumin. Besides this similarity in immunological properties, both albumin species have almost the same molecular weight and amino acid composition. Furthermore, the amino acid sequences appear to be identical apart from an additional pentapeptide at the N-terminus of the albumin-like protein. It is suggested that the albumin-like protein represents a precursor which is converted to albumin by release of a pentapeptide from the N-terminus. 相似文献