Peroxidase assay in plants: Interference by ascorbic acid and endogenous inhibitors in Sedum and Pelargonium enzyme extracts

Sedum album and Pelargonium zonale extracts do not show any peroxidase activity. Both extracts provoke a lag phase in the horse-radish peroxidase-catalyzed oxidation of guaiacol by H₂O₂. Preincubation of Sedum album extract with ascorbate oxidase eliminated completely the lag phase. Ascorbic acid has been identified as the substance responsible for this lag phase by reacting with a coloured intermediary product of the analytical reaction. In the Pelargonium zonale extract, the lag phase seems to be due to competitive inhibitors of peroxidase, which are of a phenolic nature.