Figure 2

Peroxidase activity of recombinant PfAOP in the presence of artemisinins. (a) Coupled enzymatic assays with 2.5 µM PfAOP and artemisinins as potential substrates. Activities with 100 µM tBOOH or DTBP served as controls. (b) Reversible inhibition assays in the presence of variable concentrations of artemisinins or DTBP. Activities were determined with 2.5 µM PfAOP and 50 µM tBOOH and normalized to the activities of controls without endoperoxide. (c) Time-dependent irreversible inhibition assays. PfAOP (50 µM) was preincubated with 100 µM artemisinins for up to 10 min on ice before the enzyme was diluted 1:20 in a standard coupled enzymatic assay containing 100 µM tBOOH. Activities were normalized to controls that were preincubated without peroxide. A time-dependent inactivation of PfAOP by tBOOH served as a positive control (open circles) and was compared to a potential inactivation by artemisinins (closed circles). Assays containing DMSO are labelled with an asterisk. All data are the mean ± standard deviation of at least two independent duplicate assays.