The effect of heavy metals on peroxidase from Jerusalem artichoke (Helianthus tuberosus L.) tubers

Peroxidases (EC 1.11.1.7; donor: hydrogen peroxide oxidoreductase, POD) are part of a large group of enzymes. In this study, peroxidase, a primer antioxidant enzyme, was partial purified with 2.49 fold and 29.3% efficiency from Jerusalem artichoke (Helianthus tuberosus L.) by ammonium sulphate precipitation and dialysis purification steps. The specific activity of enzyme was calculated as 612.1 EU/mg. The substrate specificity of peroxidase was investigated using 2-methoxyphenol (guaiacol)/hydrogen peroxide (H2O2) substrate pattern. Michaelis-Menten constant (K-m) and maximum velocity (V-max) values were calculated from Lineweaver-Burk graph for this substrate pattern. The enzyme had K-m values of 0.263 and 1.143 mM for guaiacol and H2O2, respectively. The enzyme had V-max of 33.3x10(5) and 0.213x10(5) EU/mL. min for guaiacol and H2O2, respectively. Also, the in vitro effect of some heavy metals such as iron (Fe2+ and Fe3+), cobalt (Co2+), strontium (Sr-2)(+), zinc (Zn2+), mercury (Hg2+), nickel (Ni2+), aluminium (Al2+) and lead (Pb2+) on POD from Jerusalem artichoke (H. tuberosus) was evaluated. These heavy metals inhibited POD acticity. IC50 values, represents the inhibitor concentration required for obtaining 50% of inhibition of peroxidase. The above mentioned metals had IC50 values of 12.58, 9.48, 12.59, 24.51, 13.57, 7.32, 10.57, 18.69 and 6.00 mM for Fe2+, Fe3+, Co2+, Sr2+, Zn2+, Hg2+, Ni2+, Al2+ and Pb2+, respectively.