翻訳と辞書 Words near each other ・ L-Photo-Leucine ・ L-pipecolate dehydrogenase ・ L-pipecolate oxidase ・ L-plan castle ・ L-plate ・ L-pop ・ L-proline amide hydrolase ・ L-R-G / The Maze / S II Examples ・ L-reduction ・ L-rhamnonate dehydratase ・ L-rhamnono-1,4-lactonase ・ L-rhamnose 1-dehydrogenase ・ L-rhamnose isomerase ・ L-Ribonucleic acid aptamer ・ L-ribulose-5-phosphate 3-epimerase ・ L-ribulose-5-phosphate 4-epimerase ・ L-Ron ・ L-saccharopine oxidase ・ L-selectin ・ L-selectride ・ L-series ・ L-serine ammonia-lyase ・ L-serine dehydratase ・ L-serine-phosphatidylethanolamine phosphatidyltransferase ・ L-seryl-tRNASec selenium transferase ・ L-Seven ・ L-shell ・ L-sit ・ L-sorbose 1-dehydrogenase ・ L-sorbose oxidase Dictionary Lists mini英和辞書 mini和英辞書 Webster 1913 Latin-English FOLDOC Wikipedia English ウィキペディア

翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク L-ribulose-5-phosphate 4-epimerase ： ウィキペディア英語版 L-ribulose-5-phosphate 4-epimerase In enzymology, a L-ribulose-5-phosphate 4-epimerase () is an enzyme that catalyzes the interconversion of ribulose 5-phosphate and xylulose 5-phosphate in the oxidative phase of the Pentose phosphate pathway. :L-ribulose 5-phosphate $\backslash rightleftharpoons$ D-xylulose 5-phosphate This enzyme has a molecular mass of 102 kDa and is believed to be composed of four identical 25.5 kDa subunits. It belongs to the family of isomerases, specifically those racemases and epimerases acting on carbohydrates and derivatives. The systematic name of this enzyme class is L-ribulose-5-phosphate 4-epimerase. Other names in common use include phosphoribulose isomerase, ribulose phosphate 4-epimerase, L-ribulose-phosphate 4-epimerase, L-ribulose 5-phosphate 4-epimerase, AraD, and L-Ru5P. This enzyme participates in pentose and glucuronate interconversions and ascorbate and aldarate metabolism. ==Enzyme Mechanism== File:Epimerase Mechanism.jpg|Mechanism of Ribulose 5-Phosphate 4-Epimerase in active site File:Aldol.jpg|Aldol and dehydration mechanims L-Ribulose 5-phosphate 4-epimerase catalyzes the epimerization of L-ribulose 5-phosphate to D-xylulose 5-phosphate by retro-aldol cleavage and subsequent aldol reaction. The proposed mechanism involves the abstraction of the proton from the hydroxyl group on C-4, followed by cleavage of the bond between C-3 and C-4 to give a metal-stabilized acetone enediolate and a glycolaldehyde phosphate fragment. The C–C bond of glycolaldehyde phosphate is then rotated 180°, and the C–C bond between C-3 and C-4 is regenerated to give inversion of stereochemistry at C-4. This mechanism is contested by a possible alternative dehydration reaction scheme. The literature〔〔 favors the aldol mechanism for two reasons. First, the retro-aldol cleavage mechanism is analogous to the reaction catalyzed by L-fuculose-phosphate aldolase which has high levels of sequence similarity with L-ribulose-5-phosphate 4-epimerase. Second, the analysis of 13C and deuterium kinetic isotope effects points toward the aldol mechanism. It has been reported that there is little to no difference in the deuterium isotope effects at C-3 and C-4, suggesting that these C–H bonds are not broken during epimerization.〔 Changes in isotope effect at C-3 would be expected for the dehydration mechanism, because the breaking of the C–H bond is the rate-limiting step in this mechanism and substituting the C-3 hydrogen with deuterium would significantly alter the rate. At the same time there are significantly large 13C isotope effects, suggesting rate-limiting C–C bond breakage, as expected with the aldol mechanism.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「L-ribulose-5-phosphate 4-epimerase」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.