Kinetic Characterization of Extracellular Catalases fromPenicillium piceum F-648 and Its Hydrogen Peroxide-Adapted Variants

A comparative kinetic study of extracellular catalases produced by Penicillium piceum F-648 and their variants adapted to H2O2 was performed in culture liquid filtrates. The specific activity of catalase, the maximum rate of catalase-induced H2O2 degradation (Vmax), Vmax/KM ratio, and the catalase inactivation rate constant in the enzymatic reaction (kin, s–1) were estimated in phosphate buffer (pH 7.4) at 30°C. The effective constant representing the rate of catalase thermal inactivation (kin*, s–1) was determined at 45°C. In all samples, the specific activity and KM for catalase were maximum at a protein concentration in culture liquid filtrates of (2.5–3.5) × 10–4 mg/ml. The effective constants describing the rate of H2O2 degradation (k, s–1) were similar to that observed in the initial culture. These values reflected a twofold decrease in catalase activity in culture liquid filtrates. We hypothesized that culture liquid filtrates contain two isoforms of extracellular catalase characterized by different activities and affinities for H2O2. Catalases from variants 5 and 3 with high and low affinities for H2O2, respectively, had a greater operational stability than the enzyme from the initial culture. The method of adaptive selection for H2O2 can be used to obtain fungal variants producing extracellular catalases with improved properties.