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Ten acylated flavonol glycosides were isolated from aqueous acetone extracts of the aerial parts of the forage legume, Onobrychis viciifolia, and their structures determined using spectroscopic methods. Among these were eight previously unreported examples which comprised either feruloylated or sinapoylated derivatives of 3-O-di- and 3-O-triglycosides of kaempferol (3,5,7,4'-tetrahydroxyflavone) or quercetin (3,5,7,3',4'-pentahydroxyflavone). The diglycosides were acylated at the primary Glc residue of O-α-Rhap(1→6)-β-Glcp (rutinose), whereas the triglycosides were acylated at the terminal Rha residues of the branched trisaccharides, O-α-Rhap(1→2)[α-Rhap(1→6)]-β-Galp or O-α-Rhap(1→2)[α-Rhap(1→6)]-β-Glcp. Identification of the primary 3-O-linked hexose residues as either Gal or Glc was carried out by negative ion electrospray and serial MS, and cryoprobe NMR spectroscopy. Analysis of UV and MS spectra of the acylated flavonol glycosides provided additional diagnostic features relevant to direct characterisation of these compounds in hyphenated analyses. Quantitative analysis of the acylated flavonol glycosides present in different aerial parts of sainfoin revealed that the highest concentrations were in mature leaflets. 相似文献
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Possible site of flavonoid synthesis in the photosynthetic apparatus (Short Communication)
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Koshi Saito 《The Biochemical journal》1974,144(2):431-432
Chloroplasts were prepared in aqueous suspension from buckwheat (Fagopyrum esculentum Moench.) seedlings, and the incorporation of [1-(14)C]acetic acid into quercetin (3,5,7,3',4'-pentahydroxyflavone) by the isolated chloroplast preparations was investigated. 相似文献
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Quercetinase (QueD) of Streptomyces sp. FLA is an enzyme of the monocupin family and catalyzes the 2,4-dioxygenolytic cleavage of the flavonol quercetin. After expression of the queD gene in Escherichia coli, high specific QueD activity was found in crude cell extracts when the growth medium was supplemented with NiCl 2 or CoCl 2, but not when Mn (2+), Fe (2+), Cu (2+), or Zn (2+) was added. The metal occupancy of Ni- and Co-QueD purified from these cells was =50%, presumably due to strong overproduction of QueD in E. coli. Circular dichroism spectroscopy indicated the same folded structure with a high content of beta-sheet for the Ni and Co protein. The apparent kinetic constants for quercetin of Ni-QueD ( k cat = 40.1 s (-1), and K m = 5.75 microM) and Co-QueD ( k cat = 7.6 s (-1), and K m = 0.96 muM) indicate similar catalytic efficiencies; however, the approximately 5-fold lower apparent K m value of Ni-QueD for dioxygen suggests that the nickel enzyme performs better under physiological conditions. The pH dependence of k cat,app indicates that an ionizable group with a p K a near 6.8 has to be deprotonated for catalysis. Electron paramagnetic resonance spectra of resting Co-QueD are indicative of a high-spin ( S = (3)/ 2) Co (2+) species in a tetrahedral or trigonal-bipyramidal coordination geometry. Anoxic binding of quercetin to QueD drastically altered the hyperfine pattern at g approximately 6 without changing the valence state of the Co(II) center and elicited a hypsochromic shift of UV-vis absorption band I of quercetin. On the basis of spectroscopic data, and considering the organic chemistry of flavonols, a nonredox role of the metal center in catalysis is discussed. 相似文献
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The plant flavonoids quercetin (3,5,7,3',4'-pentahydroxyflavone), morin (3,5,7,2',4'-pentahydroxyflavone), kaempferol (3,5,7,4'-tetrahydroxyflavone), chrysin (5,7-dihydroxyflavone), fisetin (3,7,3',4'-tetrahydroxyflavone), myricetin (3,5,7,3',4',5'-hexahydroxyflavone), myricitrin (myricetin-3-rhamnoside), hesperetin (3',5,7-trihydroxy-4'-methoxyflavanone), quercitrin (quercetin-3-L-rhamnoside), rutin (quercetin-3-rhamnosylglucoside or quercetin-3-rutinoside), and hesperidin (hesperetin-7-rutinoside) have been assayed for mutagenicity in the Salmonella/microsomal activation system. Quercetin, morin, kaempferol, fisetin, myricetin, quercitrin and rutin were mutagenic in the histidine reversion system with the frameshift strain TA98. The flavonols quercetin and myricetin are mutagenic without metabolic activation, although more effective when a rat liver microsomal preparation (S-9) is included; all others require metabolic activation. Flavonoids are common constituents of higher plants, with extensive medical uses. In addition to pure compounds, we have examined crude extracts of tobacco (snuff) and extracts from commonly available nutritional supplements containing rutin. Mutagenic activity can be detected and is correlated with the flavonoid content. 相似文献
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Procyclic acidic repetitive protein (PARP) genes located in an unusually small alpha-amanitin-resistant transcription unit: PARP promoter activity assayed by transient DNA transfection of Trypanosoma brucei. 总被引:31,自引:8,他引:23
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G Rudenko S Le Blancq J Smith M G Lee A Rattray L H Van der Ploeg 《Molecular and cellular biology》1990,10(7):3492-3504
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O-Methylated flavonoids are biosynthesized by regioselective flavonoid O-methyltransferases (OMTs), which may account for the limited number of naturally occurring flavonoids in nature. It was previously shown that poplar POMT-7 regioselectively methylates the 7-hydroxyl group of flavones, whereas rice ROMT-9 regioselectively methylates the 3'-hydroxyl group of the substrate. We co-expressed both OMT genes (POMT-7 and ROMT-9) in E. coli and carried out biotransformation experiments of some flavonoids with the transformed E. coli strain. Contrast to the predicted regioselectivity of both POMT-7 and ROMT-9, unexpected methylation reaction products, i.e. 3',4'-O-methylated flavonoids, in addition to the predicted ones, were obtained with luteolin (5,7,3',4'-tetrahydroxyflavone) and quercetin (3,5,7,3',4'-pentahydroxyflavone) as substrates. Reactions using the 3'-O-methyl derivative of luteolin and quercetin by POMT-7 revealed that the enzyme has altered its regioselectivity from the 7- to the 4'-hydroxyl groups. These results are discussed in terms of molecular modeling of POMT-7 in relation to its methyl donor. 相似文献