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911.
912.
Prostaglandin H synthase (PGHS) is an autocatalytic enzyme which plays a key role in the arachidonic acid metabolic pathway.
PGHS mediates the formation of prostaglandin H2, the precursor for a number of prostaglandins which are important in a wide variety of biological processes, including inflammation,
blood clotting, renal function, and tumorigenesis. Here we present a Michaelis-Menten-style model for PGHS. A stability analysis
determines when the reaction becomes self-sustaining, and can help explain the regulation of PGHS activity in vivo. We also
consider a quasi-steady-state approximation (QSSA) for the model, and present conditions under which the QSSA is expected
to be a good approximation. Applying the QSSA for this model can be useful in computationally intensive modeling endeavors
involving PGHS. 相似文献
913.
Anaya AL Macías-Rubalcava M Cruz-Ortega R García-Santana C Sánchez-Monterrubio PN Hernández-Bautista BE Mata R 《Phytochemistry》2005,66(4):487-494
Aqueous leachates and a CHCl3-MeOH (1:1) extract of roots of Stauranthus perforatus showed a significant phytotoxic effect on Amaranthus hypochondriacus and Echinochloa crus-galli. Bioassay-directed fractionation of the active organic extract led to the isolation and characterization of ten secondary metabolites, which included two pyranocoumarins [xanthyletin (1) and 3-(1',1'-dimethylallyl)-xanthyletin (2)], four furanocoumarins [chalepensin (3), ammirin (4), chalepin (5) and 2'-isopropyl-psoralene (6)], two lignans [asarinin (7) and fargesin (8)], one sesquiterpene [4,5-epoxi-beta-caryophyllene (9)], and one alkamide [pellitorine (10)]. From these compounds, 2'-isopropyl-psoralene (6) or anhydromarmesin, is reported for the first time as a natural product, whereas compounds 4-10 are now reported as being present in S. perforatus. Metabolites 1, 3-5 and 10 caused significant inhibition of radicle growth of A. hypochondriacus and E. crus-galli. Furthermore, in a greenhouse experiment the decomposition of the leaves and roots in the soil had a significant inhibitory effect on the growth of weeds. The allelopathic action of the decomposition of roots was evident up to the sixth week of the experiment. The effect of leaves was comparable to that of DPCA (dimethyl tetrachloroterephthalate), a commercial herbicide. Finally different concentrations of Stauranthus root powder were combined with maize kernels and used to feed corn weevil. The treatments resulted in high mortality of this insect. 相似文献
914.
915.
916.
917.
Recent reports have offered candidates for key components of the apparatus used for mechanotransduction in hair cells. TRPA1 and cadherin 23 have been proposed to be the transduction channel and component of the tip link, respectively; moreover, ankyrin repeats in TRPA1 have been proposed to be the gating spring. Although these are excellent candidates for the three components, definitive experiments supporting each identification have yet to be performed. 相似文献
918.
Tangirala RS Dixon R Yang D Ambrus A Antony S Agama K Pommier Y Curran DP 《Bioorganic & medicinal chemistry letters》2005,15(21):4736-4740
Both enantiomers of 20-fluorocamptothecin and the racemate have been prepared by total synthesis. The (R)-enantiomer is essentially inactive in a topoisomerase-I/DNA assay, while the (S)-enantiomer is much less active than (20S)-camptothecin. The lactone ring of 20-fluorocamptothecin hydrolyzes more rapidly than that of camptothecin in PBS. The results provide insight into the role of the 20-hydroxy group in the binding of camptothecin to topoisomerase-I and DNA. 相似文献
919.
Williamson RM Pietersma AL Jameson GB Parker EJ 《Bioorganic & medicinal chemistry letters》2005,15(9):2339-2342
Racemic 2-deoxyerythrose 4-phosphate was synthesized and one enantiomer of this compound was found to be a substrate for Escherichia coli 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase, the first enzyme of the shikimate pathway. When the reaction was carried out in deuterium oxide, an enzyme-catalyzed regio- and stereoselective incorporation of deuterium into the product was observed. 相似文献
920.
Targeting of amacrine cell neurites to appropriate synaptic laminae in the developing zebrafish retina 总被引:4,自引:0,他引:4
Godinho L Mumm JS Williams PR Schroeter EH Koerber A Park SW Leach SD Wong RO 《Development (Cambridge, England)》2005,132(22):5069-5079
Cellular mechanisms underlying the precision by which neurons target their synaptic partners have largely been determined based on the study of projection neurons. By contrast, little is known about how interneurons establish their local connections in vivo. Here, we investigated how developing amacrine interneurons selectively innervate the appropriate region of the synaptic neuropil in the inner retina, the inner plexiform layer (IPL). Increases (ON) and decreases (OFF) in light intensity are processed by circuits that are structurally confined to separate ON and OFF synaptic sublaminae within the IPL. Using transgenic zebrafish in which the majority of amacrine cells express fluorescent protein, we determined that the earliest amacrine-derived neuritic plexus formed between two cell populations whose somata, at maturity, resided on opposite sides of this plexus. When we followed the behavior of individual amacrine cells over time, we discovered that they exhibited distinct patterns of structural dynamics at different stages of development. During cellular migration, amacrine cells exhibited an exuberant outgrowth of neurites that was undirected. Upon reaching the forming IPL, neurites extending towards the ganglion cell layer were relatively more stable. Importantly, when an arbor first formed, it preferentially ramified in either the inner or outer IPL corresponding to the future ON and OFF sublaminae, and maintained this stratification pattern. The specificity by which ON and OFF amacrine interneurons innervate their respective sublaminae in the IPL contrasts with that observed for projection neurons in the retina and elsewhere in the central nervous system. 相似文献