- 作者: 劉鴻文 ; Thorson, Jon S. ; Miller, Vaughn P. 等
- 作者服務機構: Dept. of Chemistry, Univ. of Minnesota, Minneapolis, Minnesota, U.S.A.
- 中文摘要: Deoxy sugars are ubiquitous in nature and contribute to diverse biological activities. Attempts to design systems to control or to mimic their functions are hampered, however, by the lack of biosynthetic knowledge of these unique sugars. To elucidate the mechanism by which the sugar deoxygenation is effected, we have initiated a study to explore the biosynthesis of CDP-ascarylose, a 3,6- dideoxyhexose found in the lipopolysaccharides of Yersinia pseudotuberculosis, and our initial focus centered on C-3 deoxygenation catalyzed by E/sub 1/ and E/sub 3/. We have now purified the wild-type enzymes, cloned the corresponding genes (ascC for E/sub 1/ and ascD for E/sub 3/), and overexpressed the gene products in Escherichia coli. The purified E/ sub 3/ is a flavoprotein comprising an iron-sulfur center and E/sub 1/ is an iron- sulfur containing, pyridoxamine 5'-phosphate-dependent enzyme. Since these iron-sulfur clusters are well known one- electron carriers, reactions mediated by E/sub 1/ and E/sub 3/ must proceed via a radical mechanism. Recently, EPR analysis of E/sub 1//E/sub 3/ catalysis indicated a potential new redox role for pyridoxamine as a cofactor. These findings make this system unique from two perspectives: E/sub 1/ is the only coenzyme B/sub 6/- dependent catalyst that interacts with a sugar and not with an amino acid, and it is the first example in which coenzyme B/sub 6/ may facilitate one-electron redox chemistry. Thus, the unprecedented mechanisms of E/sub 1/ and E/sub 3/ distinguish this system as a novel radical deoxygenation with potentially interesting future developments.
- 英文摘要: --
- 中文關鍵字: Deoxysugar; Enzyme; Mechanism; Pyridoxamine; Iron-Sulfur Cluster; Free Radical; Ascarylose
- 英文關鍵字: 去氧糖類;酵素;反應機構;哆胺;鐵-硫分子團;自由基