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131.
Caffeic acid, rosmarinic acid and oligomers of caffeic acid with multiple catechol groups are all constituents of Salvia officinalis. Their antioxidant potential was investigated with regard to their radical scavenging activity and the stability and structure of the intermediate radicals. Pulse-radiolytic studies revealed very high rate constants with hydroxyl radicals. Evidence from kinetic modeling calculations suggested an unusual complex behavior due to the presence of both O4- and O3-semiquinones and formation and decay of a hydroxyl radical adduct at the vinyl side chain. The radical structures observed by EPR spectroscopy after autoxidation in slightly alkaline solutions were only partially identified due to their instability and generally represented dissociated O4-semiquinones. Hybrid density-functional calculations of the potential radical structures showed distinct differences between the resonance stabilization of the O4- and O3-semiquinones of caffeic and dihydrocaffeic acids, reflected also in the considerably faster decay of the O3-semiquinone observed by pulse radiolysis. No evidence was found for dimerization reactions via Cbeta radicals typical for lignin biosynthesis. 相似文献
132.
Kukkola EM Koutaniemi S Pöllänen E Gustafsson M Karhunen P Lundell TK Saranpää P Kilpeläinen I Teeri TH Fagerstedt KV 《Planta》2004,218(3):497-500
A specific condensed lignin substructure, dibenzodioxocin, was immunolocalized in differentiating cell walls of Norway spruce (Picea abies (L.) H. Karsten) and silver birch (Betula pendula Roth) xylem. A fluorescent probe, Alexa 488 was used as a marker on the dibenzodioxocin-specific secondary antibody. For the detection of this lignin substructure, 25-m cross-sections of xylem were viewed with a confocal laser-scanning microscope with fluorescein isothiocyanate fluorescence filters. In mature cells, fluorescence was detected in the S3 layer of the secondary wall in both tree species, but it was more intense in Norway spruce than in silver birch. In silver birch most of the signal was detected in vessel walls and less in fiber cell walls. In very young tracheids of Norway spruce and vessels and fibers of silver birch, where secondary cell wall layers were not yet formed, the presence of the dibenzodioxocin structure could not be shown.Abbreviation CLSM confocal laser-scanning fluorescence microscopy 相似文献
133.
Guo T Adang AE Dong G Fitzpatrick D Geng P Ho KK Jibilian CH Kultgen SG Liu R McDonald E Saionz KW Valenzano KJ van Straten NC Xie D Webb ML 《Bioorganic & medicinal chemistry letters》2004,14(7):1717-1720
Potent small molecule biaryl diketopiperazine FSH receptor agonists such as 10c (EC(50)=13 nM) and 11f (EC(50)=1.2 nM) were discovered through the design, synthesis and evaluation of three biaryl diketopiperazine optimization libraries with over 300 compounds. These libraries were prepared via solid-phase parallel synthesis using a cyclization-release method. 相似文献
134.
To improve the efficiency and applicability of biocatalytic redox-reactions for asymmetric ketone-reduction and enantioselective alcohol-oxidation catalyzed by nicotinamide-dependent dehydrogenases/reductases, several achievements for cofactor-recycling have been made during the last two years. First, the use of hydrogenases for NADPH recycling in a two enzyme system. Second, preparative transformations with alcohol dehydrogenases coupled with NADH oxidases for NAD+/NADP+ recycling. Third, an exceptional chemo-stable alcohol dehydrogenase can efficiently use i-propanol and acetone as cosubstrates for reduction and oxidation, respectively, in a single-enzyme system. Novel carbonyl reductases and dehydrogenases derived from plant cells are particularly suited for sterically demanding substrates. 相似文献
135.
Friedrich G Appel K Rose T Wangemann M Althaus M Rissler K 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2004,808(2):131-139
A rapid and sensitive assay for the determination of dihydroergocryptine (DHEC) in human plasma and urine samples with dihydroergotamine (DHET) as the internal standard was developed. The procedure employs on-line sample preparation using an extraction pre-column and an octadecylsilylsilica (ODS) analytical column. After centrifugation human plasma or urine were injected onto the pre-column, concentrated and extracted, back-flushed onto the analytical column and eluted with a binary methanol--aqueous formic acid gradient. Either determination of DHEC as well of its mono- and dihydroxy-metabolites was performed by measurement of the signal responses from MS detection in the selected reaction monitoring (SRM) mode using the transition of the respective parent ions to the common daughter ion at m/z=270.2 amu. The limit of quantitation (LOQ) for determinations of DHEC in both plasma and urine were 25 pg/ml for injected sample volumes of 400 microl. Proportionality of signal responses versus concentration was accomplished within the range of 25-1000 pg/ml. Recovery of target analyte from plasma was 99%. Mean values of the coefficients of variation (CV) for the target analyte in plasma ranged from 1.7 to 13.8% (within-day) and 5.0 to 9.1% (between-day) and accuracy from 91.7 to 102.6% for the within-day and from 95.8 to 98.8% for the between-day measurements. The corresponding values for determinations in urine were 1.7-14.5% (within-day) and 5.3-11.8% (between-day) for CV and 95.8-110.7% (within-day) and 100.1-104.6% (between-day) for accuracy. 相似文献
136.
Acetylcholinesterase (AChE) inhibitors are currently the only approved therapy for the treatment of Alzheimer's disease, only a limited number of drugs are commercially available. A library of non-alkaloidal natural compounds was investigated. To this end, a convenient microtitre plate method for assaying AChE inhibition, which allows a complete kinetic analysis of AChE inhibitors, was developed. Seven active compounds with Ki values in the micromolar range were identified, six of which were xanthones. This is the first report that a promising potential for AChE inhibition exists in such non-nitrogenous natural compounds. Furthermore, four xanthones among these xanthones had already been described as monoamine oxidase (MAO) inhibitors, making then dual AChE/MAO inhibitors of great interest. 相似文献
137.
The alkaloids 1',2'-didehydrostemofoline (2) and 2'-hydroxystemofoline (3) from Stemona collinsae Craib (Stemonaceae) were studied by X-ray crystallography and NMR spectroscopy, and they are compared with the parent compound stemofoline (1). The X-ray analysis of the CH2Cl2 solvate of 2'-hydroxystemofoline (3) allowed the determination of the absolute configuration of this compound unequivocally, whereas optical rotation was used to infer the absolute configuration of 1',2'-didehydrostemofoline (2). Based on these results, it is shown that asparagamine A isolated from Asparagus racemosus Willd. (Asparagaceae) is identical to 1',2'-didehydrostemofoline obtained from S. collinsae Craib, and that the reported plant source of asparagamine A was most likely a Stemona species. In the context of the current investigations, a novel concept on the biosynthesis of Stemona alkaloids has been worked out and is presented here. 相似文献
138.
Wada T Joza N Cheng HY Sasaki T Kozieradzki I Bachmaier K Katada T Schreiber M Wagner EF Nishina H Penninger JM 《Nature cell biology》2004,6(3):215-226
During the development of multicellular organisms, concerted actions of molecular signalling networks determine whether cells undergo proliferation, differentiation, death or ageing. Here we show that genetic inactivation of the stress signalling kinase, MKK7, a direct activator of JNKs in mice, results in embryonic lethality and impaired proliferation of hepatocytes. Beginning at passage 4-5, mkk7(-/-) mouse embryonic fibroblasts (MEFs) display impaired proliferation, premature senescence and G2/M cell cycle arrest. Similarly, loss of c-Jun or expression of a c-JunAA mutant in which the JNK phosphorylation sites were replaced with alanine results in a G2/M cell-cycle block. The G2/M cell-cycle kinase CDC2 was identified as a target for the MKK7-JNK-c-Jun pathway. These data show that the MKK7-JNK-c-Jun signalling pathway couples developmental and environmental cues to CDC2 expression, G2/M cell cycle progression and cellular senescence in fibroblasts. 相似文献
139.
Fierens K Geudens N Brijs K Courtin CM Gebruers K Robben J Van Campenhout S Volckaert G Delcour JA 《Protein expression and purification》2004,37(1):39-46
Triticum aestivum xylanase inhibitor I (TAXI-I) is a wheat protein that inhibits microbial xylanases belonging to glycoside hydrolase family 11. In the present study, recombinant TAXI-I (rTAXI-I) was successfully produced by the methylotrophic yeast Pichia pastoris at high expression levels (approximately 75 mg/L). The rTAXI-I protein was purified from the P. pastoris culture medium using cation exchange and gel filtration chromatographic steps. rTAXI-I has an iso-electric point of at least 9.3 and a mass spectrometry molecular mass of 42,013 Da indicative of one N-linked glycosylation. The recombinant protein fold was confirmed by circular dichroism spectroscopy. Xylanase inhibition by rTAXI-I was optimal at 20-30 degrees C and at pH 5.0. rTAXI-I still showed xylanase inhibition activity at 30 degrees C after a 40 min pre-incubation step at temperatures between 4 and 70 degrees C and after 2 h pre-incubation at room temperature at a pH ranging from 3.0 to 12.0, respectively. All tested glycoside hydrolase family 11 xylanases were inhibited by rTAXI-I whereas those belonging to family 10 were not. Specific inhibition activities against family 11 Aspergillus niger and Bacillus subtilis xylanases were 3570 and 2940IU/mg protein, respectively. The obtained biochemical characteristics of rTAXI-I produced by P. pastoris (no proteolytical cleft) were similar to those of natural TAXI-I (mixture of proteolytically processed and non-processed forms) and non-glycosylated rTAXI-I expressed in Escherichia coli. The present results show that xylanase inhibition activity of TAXI-I is only affected to a limited degree by its glycosylation or proteolytic processing. 相似文献
140.
Hiller S Kohl A Fiorito F Herrmann T Wider G Tschopp J Grütter MG Wüthrich K 《Structure (London, England : 1993)》2003,11(10):1199-1205
Signaling in apoptosis and inflammation is often mediated by proteins of the death domain superfamily in the Fas/FADD/Caspase-8 or the Apaf-1/Caspase-9 pathways. This superfamily currently comprises the death domain (DD), death effector domain (DED), caspase recruitment domain (CARD), and pyrin domain (PYD) subfamilies. The PYD subfamily is most abundant, but three-dimensional structures are only available for the subfamilies DD, DED, and CARD, which have an antiparallel arrangement of six alpha helices as common fold. This paper presents the NMR structure of PYD of NALP1, a protein that is involved in the innate immune response and is a component of the inflammasome. The structure of NALP1 PYD differs from all other known death domain superfamily structures in that the third alpha helix is replaced by a flexibly disordered loop. This unique feature appears to relate to the molecular basis of familial Mediterranean fever (FMF), a genetic disease caused by single-point mutations. 相似文献