Are colorimetric assays appropriate for measuring phenol oxidase activity in peat soils?

The activity of extracellular phenol oxidases is believed to play a critical role in decomposition processes in peatlands. The water logged, acidic conditions, and recalcitrant litter from the peatland vegetation, lead to exceptionally high phenolics in the peat. In order to quantify the activity of oxidative enzymes involved in the modification and break down of phenolic compounds two types of assays are primarily utilized: L-DOPA and ABTS. This note focuses on the strengths and weaknesses of both approaches. Both assays involve a redox reaction and the resulting oxidized chromophore is measured spectrophotometrically. However, in the presence of reducing agents such as the phenolics commonly found in peat the colorimetric reaction is reversed and cannot be used to quantify phenol oxidase activity. © 2016 Published by Elsevier Ltd. This note is motivated by the question, do we have sufficiently good assays to draw major conclusions about phenol oxidase activity in peatlands? Extracellular phenol oxidases (enzymes that oxidize phenols and consume oxygen; as defined by Sinsabaugh (2010)) are believed to play a key role for decomposition processes in peat (Fenner and Freeman, 2011; Freeman et al., 2001) yet methods for measuring their activity in peatlands haveweaknesses, not all of which have been clearly articulated. Recent reviews on assays used for measuring extracellular oxidative enzyme activity list a long array of possible interferences and shortcomings of the most common approaches (Bach et al., 2013; German et al., 2011; Sinsabaugh, 2010). Phenol oxidases have low substrate specificity and a very wide range of reactions that they can catalyze (e.g. Baldrian, 2006; Thurston,1994; Zaidi et al., 2014), which adds to the challenges in search for a specific substrate for measuring oxidative Sciences, University of Cin-