Topochemistry of the fungal degradation of lignin in birch wood as related to the distribution of guaiacyl and syringyl lignins

Summary

Samples of non-decayed birch wood and samples decayed to weight losses of 21, 44, and 67% by Coriolus versicolor were subjected to acidolysis (4h reflux in dioxane-water, 9:1 by volume, containing 0.2 M HCl). The yields of the two major products, 3-hydroxy-1-(4-hydroxy-3-methoxyphenyl)-2-propanone (ketol I) and 3-hydroxy-1-(4-hydroxy-3,5-dimethoxyphenyl)-2-propanone (ketol II), as a percentage of residual lignins, decreased progressively with increasing decay. Even so, substantial yields of I and II were obtained from the decayed wood, suggesting that during decay a considerable amount of the lignin remaining in the wood was as yet unaltered (e. g. ∼50% at a 67% weight loss). This result indicates that lignin is degraded from exposed surfaces; the decreasing yields of I and II with decay show that the surfaces become progressively larger.

The more rapid decrease in the yield of ketol II than in the yield of ketol I indicates that syringyl elements were degraded more rapidly than guaiacyl elements. The fungal enzymes, acting progressively from the lumen surfaces toward the middle lamella, encountered syringylrich lignin first.