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The Mechanism Of Inhibition Of Human Erythrocyte Catalase By Azide, Yasemi̇n Aksoy, Mevhi̇be Balk, Hamdi̇ Öğüş, Nazmi̇ Özer

Turkish Journal of Biology

In order to elucidate the kinetic mechanism of human erythrocyte catalase a well-known substrate, H_2O_2 and inhibitor azide were used. The catalase-mediated conversion of H_2O_2 to H_2O and O_2, in the presence and absence of azide, was studied in 50 mM phosphate buffer pH 7.0 at 37 ºC under conditions where the peroxidation side reaction (RH_2 + H_2O_2  R + 2H_2O) is negligible ([H_2O_2] =< 25 mM; assay time, 10 s). The kinetics conformed to the Michaelis-Menten model. Lineweaver-Burk plots for H_2O_2 at different fixed concentrations of azide were linear and intersected on the abscissa indicating a noncompetitive or irreversible type of inhibition. To identify the inhibition type Vm vs. [E] plots were constructed at different [N_3-]. The plots were linear and converged at the origin, indicating that N_3- is a noncompetitive inhibitor. Using a non-linear curve-fitting program, the kinetic parameters were calculated. The K_m value for H_2O_2, and the K_i value for azide were found to be 10.97 ± 1.46 mM and 1.107 ± 0.093 µM, respectively.