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The other enzymes are involved mainly in generat-

ing or transferring oxidants. They include glucose

oxidasewhich generates H 2 O 2 from glucose, man-

ganese peroxidasewhich oxidizes Mn (II) to Mn (III),

and which can then oxidize organic molecules, and

lignin peroxidase which catalyses the transfer of

singlet oxygen from H 2 O 2 to aromatic rings and is one

of the main initiators of attack on the lignin frame-

work. These initial oxidations involving single electron

transfers generate highly unstable conditions, setting

off a chain of chemical oxidations.

Clearly, the degradation of lignin is highly dependent

on a supply of oxygen, so it does not occur in water-

logged conditions. Lignin degradation also poses

potential hazards to the fungus because some of

the oxidative intermediates can be fungitoxic. The

white-rot fungi generate such compounds from

phenyl-propane units in vitro, but detoxify them by

234 CHAPTER 11

Fig. 11.24(a) Part of a decaying

beech stump showing dark zone

lines at the junctions between

mutually incompatible fungal

colonies. (b) A decorative wooden

bowl made from spalted (zone-

lined) beech wood. (c) Part of an

extensively degraded woody stump

showing continuous plates of melan-

izedcells within the stump tissues.

(a) (b)

(c)