Nishimoto Taiki, Matsushita Yasuyuki
Institute of Agriculture, Tokyo University of Agriculture and Technology, Tokyo 183-8509, Japan.
J Agric Food Chem. 2025 Sep 17;73(37):23369-23375. doi: 10.1021/acs.jafc.5c06517. Epub 2025 Sep 8.
The -hydroxyphenyl (H) unit is an aromatic structure found in lignin, particularly abundant in compression wood and grass, and is derived from the incorporation of -coumaryl alcohol (-CMA). Although the structural and biosynthetic aspects of lignin have been extensively studied, the polymerization reactivity of H-unit during lignification remains poorly understood. In this study, horseradish peroxidase (HRP)-catalyzed homo- and co-oxidative coupling reactions (initial stage of enzymatic dehydrogenative polymerization) with -CMA and/or coniferyl alcohol (CA) were performed to investigate monolignol consumption, dilignol formation, and their potential involvement in subsequent polymerization. The results suggest that -CMA acts as a redox shuttle mediator, promoting the dimerization of CA. Furthermore, dilignols containing a phenolic hydroxy group at the H unit showed significantly lower polymerization reactivity, suggesting that H units may exert a "capping effect" that could limit further lignin growth.
对羟基苯基（H）单元是一种存在于木质素中的芳香结构，在压缩木和草中尤为丰富，它源自对香豆醇（-CMA）的掺入。尽管木质素的结构和生物合成方面已得到广泛研究，但木质化过程中H单元的聚合反应活性仍知之甚少。在本研究中，进行了辣根过氧化物酶（HRP）催化的与-CMA和/或松柏醇（CA）的均相和共氧化偶联反应（酶促脱氢聚合的初始阶段），以研究单体木质醇的消耗、二聚木质醇的形成及其在后续聚合中的潜在作用。结果表明，-CMA充当氧化还原穿梭介质，促进CA的二聚化。此外，在H单元含有酚羟基的二聚木质醇显示出明显较低的聚合反应活性，这表明H单元可能发挥“封端作用”，从而限制木质素的进一步生长。
