EDTA inhibits peroxidase-catalyzed iodide oxidation through interaction at the iodide binding site

Abstract

EDTA inhibits the formation of I^-₃ from iodide catalysed by various pure peroxidases. The inhibition is concentration-dependent, and chloroperoxidase (CPO) is more sensitive than horseradish peroxidase (HRP) and lactoperoxidase (LPO). EDTA is more active than EGTA or other biological chelators tested. Zn₂₊, Mn₂₊ and Co₂₊ are equally active in reversing the effect of EDTA on both CPO and HRP almost completely, but ineffective in the case of LPO. The effect of EDTA on HRP can be reversed by a higher concentration of iodide but not by H₂O₂. EDTA causes a hypsochromic change in the absorption of the Soret band of HRP at 402 nm, and iodide can reverse this effect. EDTA can effectively displace radioiodide specifically bound to HRP. It is suggested that EDTA inhibits iodide oxidation by interacting at the iodide binding site of the HRP.