期刊
PHYTOCHEMISTRY
卷 66, 期 17, 页码 2001-2011出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.phytochem.2005.01.009
关键词
Quercus robur (Quercus pedunculata); Fagaceae; pedunculate oak; Rhus typhina; Anacardiaceae; staghorn sumac; Tellima grandiflora; saxifragaceae; fringe cups; biosynthesis; enzymology; hydrolyzable tannins; gallotannins; ellagitannins
Gallotannins and ellagitannins, the two subclasses of hydrolyzable tannins, are derivatives of 1,2,3,4,6-penta-Omicron-galloyl-beta-D-glucopyranose. Enzyme studies with extracts from oak leaves (Quercus robur, syn. Quercus pedunculata; Quercus rubra) and from staghorn sumac (Rhus typhina) revealed that this pivotal intermediate is synthesized from beta-glucogallin (1-Omicron-galloyl-beta-D-glucopyranose) by a series of strictly position-specific galloylation steps, affording so-called 'simple' gallotannins, i.e., mono- to pentagallyoylglucose esters. Besides its role as starter molecule, beta-glucogallin was also recognized as the principal energy-rich acyl donor required in these transformations. Subsequent pathways to 'complex' gallotannins have recently been elucidated by the isolation of five different enzymes from sumac leaves that were purified to apparent homogeneity. They catalyzed the beta-glucogallin-dependent galloylation of pentagallyoylglucose to a variety of hexa- and heptagalloylglucoses, plus several not yet characterized higher substituted analogous galloylglucoses. With respect to the biosynthesis of ellagitannins, postulates that had been formulated already decades ago were proven by the purification of a new laccase-like phenol oxidase from leaves of fringe cups (Tellima grandiflora) that regio- and stereospecifically oxidized pentagallyoylglucose to the monomeric ellagitannin, tellimagrandin II. This compound was further oxidized by a similar but different laccase-like oxidase to yield a dimeric ellagitannin, cornusiin E. (c) 2005 Elsevier Ltd. All rights reserved.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据