Substrate profiles and expression of caffeoyl coenzyme A and caffeic acid O-methyltransferases in secondary xylem of aspen during seasonal development
Substrate profiles and expression of caffeoyl coenzyme A and caffeic acid O-methyltransferases in secondary xylem of aspen during seasonal development
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DOI：
10.1023/a:1006071708728
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发表时间：
1998-11-01
影响因子：
5.1
通讯作者：
Campbell, WH
中科院分区：
文献类型：
--
作者：
Meng, H;Campbell, WH
在与咖啡酸O-甲基转移酶（EC2.1.1.104）平行的白杨发育2.1.1.68）的季节性表达。两种酶的酶活性和mRNA水平在生长季节中期达到峰值。这些结果强烈表明，这两种形式的O-甲基转移酶在生长季节积极参与木质素前体生物合成。为了确定每种酶形式的作用，木质部提取物从两天的生长季节进行了测定与四种底物：咖啡酰辅酶A，5-羟基阿魏酰辅酶A，咖啡酸和5-羟基阿魏酸。重组形式的咖啡酰辅酶A和咖啡酸O-甲基转移酶也与这些底物进行了测定。重组酶具有不同的底物特异性，咖啡酰-CoA O-甲基转移酶基本上特异于CoA酯底物，偏好咖啡酰-CoA，而咖啡酸O-甲基转移酶利用所有四种底物，偏好游离酸形式。我们认为，咖啡酰辅酶A O-甲基转移酶可能是负责生物合成的木质素前体的愈创木基途径，并可能代表一个更原始的酶形式遗留下来的非常早期的陆地植物进化。咖啡因O-甲基转移酶更可能负责甜菜碱途径中的木质素前体生物合成，特别是因为它可以非常有效地催化5-羟基阿魏酰-CoA的甲基化。后一种酶形式则可以被认为是进化上先进的植物如被子植物的木质素生物合成途径的最近进化的组分。
Seasonal expression of caffeoyl-CoA O-methyltransferase (EC 2.1.1.104) was analyzed in aspen developing secondary xylem in parallel with caffeate O-methyltransferase (EC 2.1.1.68). Enzyme activity and mRNA levels for both enzymes peaked in the middle of the growing season. These results strongly suggest that both forms of O-methyltransferase were actively participating in lignin precursor biosynthesis during the growing season. To determine the role of each enzyme form, xylem extracts from two days in the growing season were assayed with four substrates: caffeoyl-CoA, 5-hydroxyferuloyl-CoA, caffeate acid and 5-hydroxyferulic acid. Recombinant forms of caffeoyl-CoA and caffeate O-methyltransferase were also assayed with these substrates. The recombinant enzymes have different substrate specificity with the caffeoyl-CoA O-methyltransferase being essentially specific for CoA ester substrates with a preference for caffeoyl-CoA, while caffeate O-methyltransferase utilized all four substrates with a preference for the free acid forms. We suggest that caffeoyl-CoA O-methyltransferase is likely to be responsible for biosynthesis of lignin precursors in the guaiacyl pathway and may represent a more primitive enzyme form leftover from very early land plant evolution. Caffeate O-methyltransferase is more likely to be responsible for lignin precursor biosynthesis in the syringyl pathway, especially since it can catalyze methylation of 5-hydroxyferuloyl-CoA quite effectively. This latter enzyme form, then may be considered a more recently evolved component of the lignin biosynthetic pathways of the evolutionarily advanced plants such as angiosperms.