Abstract

Peroxidases (EC 1.11.1.7; donor: hydrogen peroxide oxidoreductase) are part of a large group of enzymes associated with cell wall biosynthesis, response to injury, disease, resistance and wound repair. They catalyze the oxidation of various electron donor substrates such as phenols and aromatic amines in the presence of hydrogen peroxide. In the present study, peroxidase, a primer antioxidant enzyme, was purified 9.7 fold from Turkish black radish (Raphanus sativus L.) in a yield of 2% by ammonium sulphate precipitation, dialysis and CM-Sephadex ion exchange chromatography. To check the enzyme purity, sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) was performed and a single band was observed. The substrate specificity of peroxidase was investigated using guaiacol (2-methoxyphenol). Optimum pH, optimum temperature, optimum ionic strength, stable pH, stable temperature and thermal inactivation conditions were determined for guaiacol / H₂O₂substrate pattern. These kinetic properties were found to be 6.0, 30°C, 1.0 M, 9.0, and 60°C, respectively. The molecular weight (M_w) of the enzyme was found to be 66 kDa by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS - PAGE) method. Native polyacrylamide gel electrophoresis (Native-PAGE) was performed for isoenzyme determination and a single band was observed. K_m and V_max values were calculated from Lineweaver-Burk graphs.

Key words: Turkish black radish, Raphanus sativus, peroxidase, enzyme purification, enzyme characterization.