Migrating electron holes in lignin during wood biosynthesis and biodegradation - : a hypothesis

An unsolved question in biodegradation is how ligninases can oxidize the lignin structures that are located so deep inside the compact woody cell walls, that they are inaccessible for the enzyme, due to sterical restrictions. One explanation may be that ligninases generate small diffusible agents, redox mediators, that in turn perform lignin oxidation. Parts of the cell wall structure may nevertheless be too compact even for these, and some enzymes seem to interact directly with the lignin. The present paper discusses the hypothesis that the enzymatically generated aromatic radicals in lignin can oxidize other aromatic structures within the polymer. A chain-reaction may be therefore created, that allows the electron-holes to migrate, probably facilitated by some flexibility of the lignin. Thus, the eventual depolymerization of lignin may possibly occur far apart from the initial oxidation site. The migrating electron hole theory might be also applied on lignin biosynthesis.