Figure 1.

H₂O₂-dependent peroxidase activity of cytochrome c. After adding up to 500 μm H₂O₂ to 5 μm cyt c, the formation of ABTS^+• from 1 mm ABTS in 10 mm PB, pH 7.4, was followed for up to 3 h at 37 °C by monitoring the absorbance increase at 734 nm. The kinetic curves in A illustrate that in the presence of increasing H₂O₂ concentrations (straight lines; 25, 50, 100, 250 and 500 μm) a shorter lag phase, a higher linear ABTS^+• formation rate, and a quicker deactivation of the cyt c–based peroxidase activity were observed. In B, the linear increase of the cyt c–derived enzymatic activity with H₂O₂ concentration is shown. In C, the coinciding exponential decrease in the relative efficiency of the cyt c-derived peroxidase activity is illustrated. In A, averaged kinetic curves from three independent experiments are shown; in B and C, the corresponding mean (points) and S.D. (error bars) values are given.