Effects of metal ions on the activity and stability of peroxidase in Tartary buckwheat shoots

This is the first report to purify and characterize POX in shoots of buckwheat species. POX was partially purified from Tartary buckwheat shoots by 48.0 fold with a final yield of 9.07%. During ion-exchange and gel filtration chromatography, only one peak corresponding to POX activity was found. The molecular weight of POX was determined to be 37.5 kDa using gel filtration chromatography. The optimal pH of POX activity was 5.5 (guaiacol, quercetin) and 5.0 (ABTS). The Km of POX activity was 22.3 mM (guaiacol), 6.3 mM (ABTS) and 0.92 mM (quercetin). In contrast, the Km for quercetin in the presence of Fe ions was two orders of magnitude less (0.018 mM) than that in its absence. The stability of POX activity was increased in the presence of trivalent metal ions, even after 186 h in solution. POX activity was retained by 83.6% and 56.1% in the presence of 1 mM Fe and Al ions, respectively, whereas it was completely inactivated in their absence. To the best of our knowledge, this is the first study to detail the activation and stabilization of POX activity in relation to trivalent metal ions.