Studies on the Biosynthesis of Lignin

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Abstract
1. Dehydrogenative polymerization product (DHP) was obtained from coniferyl alcohol by the action of purified bamboo shoot peroxidase [EC 1.11.1.7] and found to give similar properties to that of native lignin except that it had a lower molecular weight (approx. 1,000). 2.Two methods for determination of the rate of DHP formation were described, namely spectrophotometric measurements of the rate of disappearance of coniferyl alcohol and the formation of DHP. 3. Not only bamboo shoot peroxidase but also wheat germ and horseradish peroxidases were found to form DHP, indicating that plant peroxidase generally participates in the formation of DHP. 4. The rate of DHP formation was dependent on the concentrations of peroxidase, hydrogen peroxide and coniferyl alcohol The disappearance of coniferyl alcohol in the peroxidatic reaction was inhibited by KCN, while the polymerization step was not. These results indicated that hydrogen peroxide and peroxidase are essential for dehydrogenation of coniferyl alcohol while the subsequent polymerization process occurs nonenzymatically. 5. The reactivities of peroxidase with coniferyl alcohol analogs were studied and the essential groups in the molecule of substrate for dehydrogenation and polymerization were confirmed to be a free phenolic OH group and a double bond in the side chain. 6. Attempts to increase the molecular weight of DHP formed in the enzymatic reaction were unsuccessfuL 7. Based on these results, the mechanism of formation of DHP and its relation to lignification were discussed.

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