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.

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