Kinetics of catalase inactivation induced by ultrasonic cavitation

Kinetic patterns of sonication-induced inactivation of bovine liver catalase (CAT) were studied in buffer solutions (pH 4.0-11.0) within the temperature range from 36 to 55degreesC. Solutions of CAT were exposed to LF (20.8 kHz) ultrasound (specific power, 48-62 W/cm(2)). The kinetics of CAT inactivation was characterized by effective first-order rate constants (s(-1)) of total inactivation (k(in)), thermal inactivation (*k(in)), and ultrasonic inactivation (k(in)(us)). In all cases, the following inequality was valid: k(in) > *k(in). The value of k(in)(us) increased with the ultrasound power (range, 48-62 W/cm(2)) and exhibited a strong dependence on the pH of the medium. On increasing initial concentration of CAT (0.4-4.0 nM), k(in)(us) decreased. The three rate constants were minimum within the range pH 6.5-8.0; their values increased considerably at pH < 6.0 and pH > 9.0. At 36-55degreesC, the temperature dependence of k(in)(us) was characterized by an activation energy (E-act) of 19.7 kcal/mol, whereas the value of E-act for CAT thermoinactivation was equal to 44.2 kcal/mol. Bovine and human serum albumins (BSA and HSA, respectively) inhibited sonication-induced CAT inactivation; complete prevention was observed at concentrations above 2.5 mug/ml. Dimethyl formamide (DMFA), a scavenger of hydroxyl radicals (HO.), prevented sonication-induced CAT inactivation at 10% (k(in) and *k(in) increased with the content of DMFA at concentrations in excess of 3%). The results obtained indicate that free radicals generated in the field of ultrasonic cavitation play a decisive role in the inactivation of CAT, which takes place when its solutions are exposed to low-frequency ultrasound. However, the efficiency of CAT inactivation by the radicals is determined by (1) the degree of association between the enzyme molecules in the reaction medium and (2) the composition thereof.