Phenol Oxidation

Abstract

Lignins are major structural components of plant cell walls and hence of plant litter. The complex polymer effectively resists chemical and enzymatic attack, even more than other important phenolic litter constituents such as condensed tannins. The enzymatic degradation of both lignin and condensed tannins depends on the oxidation of aromatic rings. Since some of the enzymes catalyzing these reactions exhibit a degree of substrate specificity, the oxidation of different phenolic compounds involves different classes of phenol oxidases. This chapter describes a method for quantifying the activity of phenol-oxidizing enzymes based on the determination of increases in oxidation products. The approach potentially covers the combined activities of several enzymes with different substrate affinities. Specifically, a buffered extract from plant litter, animal gut content, or another type of environmental sample is added to a solution of a suitable phenolic substrate. Its oxidation is followed over time as an increase in brown coloration determined spectrophotometrically at 520 nm, while suppressing polymerization of the quinonic oxidation products. Since those oxidation products are not precisely defined, the described method yields information only on the relative phenol oxidation capacity. Therefore, meaningful comparisons are restricted to data obtained from identical substrates.