White-rot fungi have developed nonspecific mechanisms for degrading lignin, according to Aust. Most of the mechanisms depend on heme-containing peroxidases secreted by the fungi. In the presence of hydrogen peroxide, which the fungi also produce in various ways, peroxidases promote the one-electron oxidation of substrates to free radicals. The nonspecificity and the availability of multiple mechanisms are apt for lignins, which are believed to be structurally highly irregular. Also supporting this approach is the nature of the protective effect of components of various woods.
Some woods are durable because of compounds called extractives.
But Schultz and Nicholas have found that they are less effective fungicides than commercial biocides. However, they are excellent free-radical scavengers. Schultz and Nicholas have suggested that extractives must have both antifungal and antioxidant activities to impart durability. BHT alone offers little protection against fungi, they have found. But BHT combined with a biocide affords more protection than the biocide alone.