Purification and characterization of an intracellular peroxidase from genetically transformed roots of red beet (Beta vulgaris L.)

An intracellular peroxidase (POD) produced by genetically transformed root cultures of red beet (Beta vulgaris L.) was purified using a combination of (NH4)2SO4 fractionation and ion exchange chromatography resulting in 15-fold enhancement of activity. This enzyme exhibited highest activity (10,500 U mg−1 protein) and stability at pH 5.0 and retained over 70% of the activity for 20 min at 70 °C where horseradish peroxidase (HRP) – a vastly used commercial source, had lost its activity after 11 min. The purified enzyme showed highest preference for H2O2 as the substrate (Km value of 0.1). Among the H donors, the enzyme appeared to have affinity in the order of orthodianisidine > 2,2′-azino-bis(3-ethylbenz-thiazoline)-6-sulfonic acid > guaiacol. The purified POD was completely and competitively inhibited by periodate (HIO6-, Ki = 0.2 mM) whereas sodium azide (NaN3) was a non-competitive inhibitor. The purified POD had a molecular mass of 45 kDa as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and activity staining. This is the first report describing purification and characterization of POD from red beet hairy roots showing its better efficacy than commercial HRP.