Properties of Two Anionic Peroxidase Isoenzymes from Turnip (Brassica napus L.) Roots

Two anionic peroxidase isoenzymes of turnip (Brassica napus L.) roots (A1 and A2) have been partially purified to study some properties which may be beneficial for their use in clinical and enzyme immunoassays. Both isoenzymes showed similar thermostability in preincubation tests or storage at 0−4 °C and −20 °C, which was comparable to that reported for other peroxidase isoenzymes. The optimum pH for the reaction with ABTS as substrate was 4.3 for both isoenzymes while it was 5.3 for A1 and 4.6 for A2 when o-dianisidine is used. Isoenzyme A1 showed higher affinities for the substrates o-dianisidine (K m 0.25 mM) and ABTS (S 0.5 50 μM) than A2 (K m 0.37 mM and S 0.5 158 μM, respectively). Nevertheless the affinity of both isoenzymes for ABTS was 80 and 25 times higher, respectively, than that described for commercially available anionic peroxidases. Keywords: Brassica napus L.; peroxidase isoenzymes; turnip