Two Different O-Demethylation Enzymic Systems in Lignin Metabolism of Soil Bacterium and Clonig of Lignin Biphenyl Specific O-Demethylase Gene

从生物圈中分离到一种以丁香酸盐、香草酸盐和5,5′-脱氢双苯基木质素为唯一来源的木素二聚体化合物Sphingomonas paucimobilis SYK-6。我们之前的研究已经确定了DDVA等二聚体化合物的代谢途径及其许多必需基因，但对丁香酸、香草酸和DDVA（木质素联苯化合物）的o -去甲基化反应尚未进行研究。在本研究中，我们发现丁香酸和香草酸的o -去甲基化是四氢叶酸（THF）依赖的甲基转移酶反应体系，而S paucimobilis SYK-6的THF依赖酶对DDVA（木质素联苯化合物）没有活性。我们还发现，在S paucimobilis SYK-6中，DDVA o -去甲基化是一个氧合性去甲基化系统，如细胞色素P-450，并且在Sphingomonas paucimobilis SYK-6中存在两种不同的去甲基化系统。本研究成功克隆了S paucimobilis SYK-6中负责DDVA o -去甲基化的基因（ligX）。

Sphingomonas paucimobilis SYK-6, a bacterium that can grow on various lignin dimeric compounds that include syringate, vanillate and 5,5'-dehydrodivanillate (DDVA, lignin biphenyl compound) as a sole source, was isolated from biosphere. The metabolic pathways of DDVA and other dimeric compounds and the many essential genes for the pathways have been identified in our previous studies, however the O-demethylation reactions for syringate, vanillate and DDVA(lignin biphenyl compound) have not been investigated.In this study, we show that the O-demethylation of syringate and vanillate is the tetrahydrofolate(THF)-dependent methyltransferase reaction system, whereas the THF-dependent enzyme of S paucimobilis SYK-6 has no activity on DDVA(lignin biphenyl compound). We also show that DDVA O-demethylation in S paucimobilis SYK-6 is an oxygenative demethylase system such as cytochrome P-450 and show that two different demethylation systems exist in Sphingomonas paucimobilis SYK-6. In this study, we succeed molecular cloning the gene (ligX) responsible for the DDVA O-demethylation in S paucimobilis SYK-6.