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31.
Kyohei SatoAtsushi Minami Toyoyuki OseHiroki Oguri Hideaki Oikawa 《Tetrahedron letters》2011,52(41):5277-5280
Enzymatic epoxide-opening cascade is one of the key biosynthetic processes for constructing structurally diverse polyethers. Here we report the first in vitro analysis of the cyclization catalyzed by two epoxide hydrolases, MonBI and MonBII involved in monensin biosynthesis, using simple epoxy-alcohols and the unprecedented synergistic effect on the epoxide-opening activity between these epoxide hydrolases. 相似文献
32.
Xixi Wang Jiankai Shan Wei Liu Jing Li Hongwei Tan Xichen Li Guangju Chen 《Molecules (Basel, Switzerland)》2021,26(13)
In this work, we have investigated the binding conformations of the substrate in the active site of 5-HIU hydrolase kpHIUH and its catalytic hydrolysis mechanism. Docking calculations revealed that the substrate adopts a conformation in the active site with its molecular plane laying parallel to the binding interface of the protein dimer of kpHIUH, in which His7 and His92 are located adjacent to the hydrolysis site C6 and have hydrogen bond interactions with the lytic water. Based on this binding conformation, density functional theory calculations indicated that the optimal catalytic mechanism consists of two stages: (1) the lytic water molecule is deprotonated by His92 and carries out nucleophilic attack on C6=O of 5-HIU, resulting in an oxyanion intermediate; (2) by accepting a proton transferred from His92, C6–N5 bond is cleaved to completes the catalytic cycle. The roles of His7, His92, Ser108 and Arg49 in the catalytic reaction were revealed and discussed in detail. 相似文献
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37.
Hao Zuo Chen Zhang Yang Zhang Prof. Dawen Niu 《Angewandte Chemie (International ed. in English)》2023,62(42):e202309887
Here we report a simple and general method to achieve fully unprotected, stereoselective glycosylation of carboxylic acids, employing bench-stable allyl glycosyl sulfones as donors. Running the glycosylation reaction under basic conditions was crucial for the efficiencies and selectivities. Both the donor activation stage and the glycosidic bond forming stage of the process are compatible with free hydroxyl groups, thereby allowing for the use of fully unprotected glycosyl donors. This transformation is stereoconvergent, occurs under mild and metal-free conditions at ambient temperature with visible light (455 nm) irradiation, and displays remarkable scope with respect to both reaction partners. Many natural products and commercial drugs, including an acid derived from the complex anticancer agent taxol, were efficiently glycosylated. Experimental studies provide insights into the origin of the stereochemical outcome. 相似文献
38.
A series of novel amide derivatives bearing an indazole moiety were synthesized and evaluated for their in vitro S-adenosyl-L-homocysteine hydrolase (SAHase) inhibitory activity. Among these compounds, 8b, 8m, 8r and 8w showed better or similar inhibitory effects compared to the positive control aristeromycin. These results provide a novel lead for the discovery of more potent non-adenosine analogs as SAHase inhibitors. 相似文献
39.
Jordan DB Li XL Dunlap CA Whitehead TR Cotta MA 《Applied biochemistry and biotechnology》2007,141(1):51-76
β-d-Xylosidase from Selenomonas ruminantium is revealed as the best catalyst known (k
cat, k
cat/K
m) for promoting hydrolysis of 1,4-β-d-xylooligosaccharides. 1H nuclear magnetic resonance experiments indicate the family 43 glycoside hydrolase acts through an inversion mechanism on
substrates 4-nitrophenyl-β-d-xylopyranoside (4NPX) and 1,4-β-d-xylobiose (X2). Progress curves of 4-nitrophenyl-β-d-xylobioside, xylotetraose and xylohexaose reactions indicate that one residue from the nonreducing end of substrate is cleaved
per catalytic cycle without processivity. Values of k
cat and k
cat/K
m decrease for xylooligosaccharides longer than X2, illustrating the importance to catalysis of subsites −1 and +1 and the
lack there of subsite +2. Homology models of the enzyme active site with docked substrates show that subsites bey ond−1 are
blocked by protein and subsites bey ond +1 are not formed; they suggest that D14 and E186 serve catalysis as general base
and general acid, respectively. Individual mutations, D14A and E186A, erode k
cat and k
cat/K
m by <103 and to asimilar extent for substrates 4NPX and 4-nitrophenyl-α-l-arabinofuranoside (4NPA), indicating that the two substrates share the same active site. With 4NPX and 4NPA, pH governs k
cat/K
m with pK
a values of 5.0 and 7.0 assigned to D14 and E186, respectively. k
cat (4NPX) has a pK
a value of 7.0 and k
cat (4NPA) is pH independent above pH 4.0, suggesting that the catalytically inactive, “dianionic” enzyme form (D14-E187-) binds
4NPX but not 4NPA.
The mention of firm names or trade products does not imply that they are end orsed or recommended by the US Department of
Agriculture over other firms or similar products not mentioned. 相似文献
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