Purification and partial characterization of a thermostable peroxidase isoenzyme from Bambara groundnut (Vigna subterranea L. Verdc) seedlings

Thermostable isoperoxidases, especially peroxidase A6, have already been found in seedlings of Vigna sp, indicating their potential for biotechnological applications. In this study, peroxidase A6 was purified from the roots of Bambara groundnut (Vigna subterranea L. Verdc) seedlings by a combination of gel filtration on Sephadex G-100, heat treatment, and ion exchange chromatography on CM cellulose and DEAE cellulose. The 41-kDa enzyme shows high catalytic efficiency in the oxidation of O-dianisidine, ABTS, TMB, DAB and OPD at acidic pH optimum and the reduction of H₂O₂. It has an optimum temperature of activity of 60 °C and a calculated activation energy of 221.5 KJ/mol for its thermal inactivation at pH 8. Mg²⁺ inhibits the enzyme. Ca²⁺ strongly increases its thermal stability, while Mn²⁺ and Zn²⁺ decrease it. The enzyme is inhibited by sodium azide at concentrations above 1 µM, with an IC₅₀  value of about 10 µM. This inhibition, in addition to the RZ value of 2.4 (A_403nm/A_280nm), confirms the presence of a haem group in the active site, which is common for class III plant peroxidases. Due to its unique catalytic and thermal properties, peroxidase A6 has the potential to be a valuable tool for various biotechnological applications, especially for enzyme immunoassays and clinical diagnosis.