Selective oxidation of enzyme extracts for improved quantification of peroxidase activity

Natural components endogenous to plant material extracts often interfere with traditional peroxidase assays by reducing the oxidized product generated as a result of the peroxidase-catalyzed reaction. This leads to an underestimation of peroxidase activity when the oxidized product provides the signal for enzyme activity quantification. This article describes a relatively simple way to alleviate complications arising due to the presence of such confounding compounds. The method is based on using 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) as the reducing substrate. The oxidized product of the reaction is ABTS(+), the accumulation of which can be followed spectrophotometrically. It is shown here that one can selectively inactivate the endogenous compounds that confound the peroxidase assay by treating the enzyme preparation with the oxidized product itself, ABTS(+), prior to initiating the quantification assay. This approach is selective for those compounds likely to interfere with peroxidase quantification. The presented method is shown to alleviate the complications associated with lag phases typical of plant extract peroxidase assays and, thus, to more accurately reflect total peroxidase activity. The presented assay is expected to be applicable to the wide range of biological systems for which the determination of peroxidase activity is desired.