ABSTRACT
This chapter attempts to approach the complex problem of lignin biodegradation through stereobiochemistry, by making clear the significance of the nonstereospecificity of peroxidase and laccase. Lignin is the most unusual of all natural products in that it is optically inactive even with the presence of asymmetric carbon atoms in its molecule, which is in striking contrast to other naturally occurring chiral biopolymers, such as nucleic acids, proteins, and polysaccharides. All biological processes consist of systematic chain reactions achieved by “enzyme conveyer routes” regardless of whether concerned with biosynthesis or biodegradation of natural products, so that metabolism is directed toward correct destinations interrelated with the whole biological recycling system. The significance of a nonstereospecific oxidation of lignin with radical species produced by laccase/O2 or peroxidase/H2O2 was investigated in relation to the degradation of the optically inactive lignin polymer. Lignin is known to be degraded by white-rot fungi regardless of whether they produce readily detectable extracellular phenol-oxidizing enzymes.
