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排序方式: 共有243条查询结果,搜索用时 15 毫秒
1.
Don Trinh Nguyen Jens Christian G?pfert Nobuhiro Ikezawa Gillian MacNevin Meena Kathiresan Jürgen Conrad Otmar Spring Dae-Kyun Ro 《The Journal of biological chemistry》2010,285(22):16588-16598
Sesquiterpene lactones are characteristic natural products in Asteraceae, which constitutes ∼8% of all plant species. Despite their physiological and pharmaceutical importance, the biochemistry and evolution of sesquiterpene lactones remain unexplored. Here we show that germacrene A oxidase (GAO), evolutionarily conserved in all major subfamilies of Asteraceae, catalyzes three consecutive oxidations of germacrene A to yield germacrene A acid. Furthermore, it is also capable of oxidizing non-natural substrate amorphadiene. Co-expression of lettuce GAO with germacrene synthase in engineered yeast synthesized aberrant products, costic acids and ilicic acid, in an acidic condition. However, cultivation in a neutral condition allowed the de novo synthesis of a single novel compound that was identified as germacrene A acid by gas and liquid chromatography and NMR analyses. To trace the evolutionary lineage of GAO in Asteraceae, homologous genes were further isolated from the representative species of three major subfamilies of Asteraceae (sunflower, chicory, and costus from Asteroideae, Cichorioideae, and Carduoideae, respectively) and also from the phylogenetically basal species, Barnadesia spinosa, from Barnadesioideae. The recombinant GAOs from these genes clearly showed germacrene A oxidase activities, suggesting that GAO activity is widely conserved in Asteraceae including the basal lineage. All GAOs could catalyze the three-step oxidation of non-natural substrate amorphadiene to artemisinic acid, whereas amorphadiene oxidase diverged from GAO displayed negligible activity for germacrene A oxidation. The observed amorphadiene oxidase activity in GAOs suggests that the catalytic plasticity is embedded in ancestral GAO enzymes that may contribute to the chemical and catalytic diversity in nature. 相似文献
2.
Initial steps in the degradation of benzene sulfonic acid, 4-toluene sulfonic acids,and orthanilic acid in Alcaligenes sp. strain O-1 总被引:2,自引:0,他引:2
Thomas Thurnheer Daniel Zürrer Otmar Höglinger Thomas Leisinger Alasdair M. Cook 《Biodegradation》1990,1(1):55-64
Alcaligenes sp. strain O-1 grew with benzene sulfonate (BS) as sole carbon source for growth with either NH4
+ or NH4
+ plus orthanilate (2-aminobenzene sulfonate, OS) as the source(s) of nitrogen. The intracellular desulfonative enzyme did not degrade 3- or 4-aminobenzene sulfonates in the medium, although the enzyme in cell extracts degraded these compounds. We deduce the presence of a selective permeability barrier to sulfonates and conclude that the first step in sulfonate metabolism is transport into the cell. Cell-free desulfonation of BS in standard reaction mixtures required 2 mol of O2 per mol. One mol of O2 was required for a catechol 2,3-dioxygenase. When meta ring cleavage was inhibited with 3-chlorocatechol in desalted extracts, about 1 mol each of O2 and of NAD(P)H per mol of BS were required for the reaction, and SO3
2- and catechol were recovered in high yield. Catechol was shown to be formed by dioxygenation in an experiment involving 18O2. 4-Toluene sulfonate was subject to NAD(P)H-dependent dioxygenation to yield SO3
2- and 4-methylcatechol, which was subject to meta cleavage. OS also required 2 mol of O2 per mol and NAD(P)H for degradation, and SO3
2- and NH4
+ were recovered quantitatively. Inhibition of ring cleavage with 3-chrorocatechol reduced the oxygen requirement to 1 mol per mol of OS SO3
2- (1 mol) and an unidentified organic intermediate, but no NH4
+, were observed. 相似文献
3.
4.
In addition to known derivatives, four new sesquiterpene-coumarin ethers were isolated from the roots of Achillea ochroleuca and Artemisia tripartita and identified by 1H and 13C NMR spectroscopy, including lanthanide induced shifts. The new compounds are isofraxidin derived ethers which differ from the previously described derivatives by ring cleavage and methyl migration within the terpenoid unit. The chemosystematic importance of sesquiterpene-coumarin ether accumulation within the two genera is briefly discussed. 相似文献
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7.
The last step in the biosynthesis of cyanogenic glucosides, the glucosylation of the cyanohydrin intermediate, has been investigated in detail using Triglochin maritima seedlings. The glucosyltransferase activity is not associated with membranes and appears to be a "soluble" enzyme. The cyanohydrin intermediate, which is formed by hydroxylation of 4-hydroxyphenylacetonitrile by a membrane-bound enzyme, is free to equilibrate in the presence of the glucosyltransferase and UDPG, because it can be trapped very efficiently. This indicates that this intermediate is not channeled (unlike some of the other intermediates), although it is probably the most labile of all of them. The glucosyltransferase of T. maritima responsible for the glucosylation of the cyanohydrin was separated from another glucosyltransferase, which used 4-hydroxybenzylalcohol as a substrate, and purified over 200-fold. It catalyzed the glucose transfer from UDPG to only 4-hydroxymandelonitrile and 3,4-dihydroxymandelonitrile, giving rise to the respective cyanogenic glucosides. Although the activities with these two substrates behaved differently in certain respects (e.g., extent of inactivation during purification and difference in activation by higher salt concentrations), most of the data acquired favor the view that only one enzyme in T. maritima is responsible for the glucosylation of both substrates. 相似文献
8.
Rhodopseudomonas sulfoviridis is unable to grow with sulfate as sole sulfur source. Radioactively labelled sulfate is not incorporated into the cells. Growth only occurs in the presence of reduced sulfur compounds, such as sulfide, thiosulfate, elemental sulfur and cysteine. ATP sulfurylase, adenylylsulfate kinase, O-acetylserine sulfhydrylase and cysteine desulfhydrase are present. Adenylylsulfate sulfotransferase and thiosulfonate reductase are lacking. The enzymes of the sulfate-activating system are not derepressed by O-acetylserine.Non common Abbreviations APS
Adenosine 5-phosphosulfate
- PAPS
3-phosphoadenosine 5-phosphosulfate 相似文献
9.
Investigations on growth inhibition in Helianthus annuus led to the isolation of a new sesquiterpene lactone, a germacranolide with an α-methylene-γ-lactone moiety. The structure of this new germacranolide, annuithrin, was elucidated by spectroscopic methods. Its biological activity has been proven by growth inhibition in straight growth tests, antibacterial tests and inhibition of DNA-/RNA-synthesis in cells of the ascitic form of Ehrlich carcinoma. 相似文献
10.