Ultrasonic and Thermal Inactivation of Catalases from Bovine Liver,the Methylotrophic Yeast Pichia pastoris,and the Fungus Penicillium piceum

The kinetics of inactivation of catalases from bovine liver (CAT), the fungus Penicillium piceum (CAT1), and the methylotrophic yeast Pichia pastoris (CAT2) was studied in phosphate buffer (pH 5.5 or 7.4) at 45 and 50°C or under the conditions of exposure to low-frequency ultrasound (LFUS; 27 kHz, 60 W/cm²). The processes were characterized by effective first-order rate constants (s^?1): k _in (total inactivation), k ^*_in (thermal inactivation), and k ^*_in (us) (ultrasonic inactivation). The values of k _in and k ^*_in increased in the following order: CAT1 < CAT < CAT2. Circular dichroic spectra of the enzyme solutions were recorded in the course of inactivation by high temperatures (45 and 50°C ) and LFUS, and the contents of secondary structures were calculated. Processes of thermal and ultrasonic inactivation of catalases were associated with a decrease in the content of α helices and an increase in that of antiparallel β structures and irregular regions (CAT1 < CAT < CAT2). We conclude that the enzymes exhibit the following rank order of resistance: CAT1 > CAT > CAT2. Judging from the characteristics of CAT1, it appears to be an optimum component for antioxidant enzyme complexes.