The mechanism of biosynthesis of plant cell walls

本研究旨在研究参与高等植物细胞壁的阿拉伯半乳糖蛋白(AGPs)的生物合成机制，并通过其糖链的器官特异性表达来评估它们在组织分化中的生理作用。为了达到这一目的，本论文在对酶活性和酶性质进行了专一性测定的基础上，结合对α-L岩藻糖基转移酶(α-L-岩藻糖基转移酶)在亚细胞组织中的定位，对其进行了研究。1.以β-L-岩藻糖基转移酶为糖供体，以2-氨基吡啶(AGG-PA)衍生的α-α1*3Galbeta1*6半乳糖为受体底物，以萝卜初生根的微球(粗膜)组分为酶来源，构建了反应体系。2.酶性质：该酶在pH 6.0-7.5和25oC时酶活最高，需要Zwittergent和Mn21&gt；或mg^2，其Km值分别为0.08mM和3.72mM。岩藻糖基化的AgG-PA的化学和酶分析证实，L-Fuc通过α-糖苷键与阿拉伯糖基连接在0-2位。

This study is aimed to investigate the mechanism of the biosynthesis of arabinogalactan-proteins (AGPs) involved in cell walls of higher plants, and to evaluate their physiological roles concerning to tissue differentiation in relation to the organ specific expression of their sugar chains. To approach this purpose, alpha-L-fucosyltransferse (alpha-L-FucTase), an enzyme catalyzing the transfer of L-fucose (L-Fuc) residues, is focused based on its specific assay for enzyme activity and enzymatic properties, in addition to the localization of the enzyme in sub cellular organs.1.The reaction mixture was constructed by GDP-L-Fuc as the sugar donor and and Araalpha1*3Galbeta1*6Gal derivatized with 2-aminopyridine (AGG-Pa) as the acceptor substrate together with the microsome (crude membrane) fraction as the enzyme source obtained from 6-d-old radish primary roots. After incubation at 25C,the enzyme activity was assayd by estimation of the transferred product separated by HPLC.The enzyme assay EAS also done by using GDP-L- [^<14>C] -Fuc in order to estimate the tranfer action into high molecular weight compounds.2.The enzyme properties : The enzyme is maximally active at pH6.0-7.5 and at 25oC,and requires Zwittergent and Mn^<21> or Mg^2. The km values are estimated to be 0.08 and 3.72mM for GDP-L-Fuc and AGG-PA,respectively. Chemical and enzymatic analyzes of fucosylated AGG-PA confirmed the attachment of L-Fuc to the arabinosyl residue at 0-2 by alpha-glycosidic linkage.