Full Length Research Paper

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

İhsan Güngör Şat

Department of Food Engineering, Agricultural Faculty, Atatürk University, 25240-Erzurum, TR-Turkey, E-mail: igsat@atauni.edu.tr. Tel: +90 442 2312481. Fax: +90 442 2360958.

Accepted 1 May, 2008

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 33.3x10⁵ and 0.213x10⁵ 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 (Sr²)⁺, 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.

Key words: Jerusalem artichoke, Helianthus tuberosus, peroxidase; enzyme, metal ions, inhibition.