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Stabilizing and Suicide-Peroxide Protecting Effect of Ni²⁺ on Horseradish Peroxidase

K. Nazari ^a,b,*, A. Mahmoudi^c, R. Khodafarin^b, A.A. Moosavi-Movahedi^a and A. Mohebi^c

^a Institute of Biochemistry and Biophysics, University of Tehran, P.O. Box 13145/1384, Tehran, Iran
^b Research Institute of Petroleum Industry, N.I.O.C., P.O. Box 18745/4163, Tehran, Iran
^c Islamic Azad University, Karaj Branch, Karaj, Iran P.O. Box 31485/2-313

The present research discusses the structure stabilizing and protecting effects of Ni²⁺ against suicide-peroxide inactivation of horseradish peroxidase (HRP). Suicide inactivation of HRP by hydrogen peroxide (3 mM) was monitored by measuring change in the absorbance of the colored product (tetraguaiacol) of the catalytic reaction cycle at 470 nm. Progress curves of the catalytic reaction cycle were obtained at 27 °C, phosphate buffer (5 mM), pH 7.0. The corresponding kinetic parameters (e.g., initial enzyme activity (α_o) and the apparent rate constant (k_i) of suicide inactivation of HRP by peroxide) were evaluated using a kinetic equation derived in this study. Comparative activatory and inhibitory effects of Ni²⁺ on the kinetics of suicide-peroxide inactivation of HRP are discussed.

Keywords: Horseradish Peroxidase, Suicide inactivation, Enzyme protection, Ni²⁺