Action of shear on enzymes: studies with catalase and urease

Intermittent shear was applied to approximately 1 mg/ml solutions of bovine liver catalase in a coaxial cylindrical viscometer at temperatures from 20 to 60°C and shear rates up to 683 sec^?1. The viscometer was sealed to prevent evaporation. Up to 40°C there were no activity losses during 3 hr total shearing. Above 40°C shearing reduced losses due to thermal inactivation, possibly by interfering with precipitation. At 3440 sec^?1 and 40°C fine precipitates formed but little activity was lost. No activity losses were found with experimental conditions under which Taylor vortexing occurred, nor when shear stresses were increased up 57 times by adding glycerol to raise the, viscosity. There were no significant losses in a capillary rheometer at shear rates up to 10⁶ sec^?1. When low concentration (6 μg/ml) catalase solutions were sheared there was little loss in sealed systems, but there were losses in “open” systems even in low-temperature nonshear experiments. Although there were no losses with 1 mg/ml solutions, 6 μg/ml catalase solutions from an alternative source did lose activity in sealed systems but much less than expected from previously published work. Approximately 1 mg/ml jack bean urease solutions were sheared in the sealed system at 23°C and 683 sec^?1 for 3 hr. No losses were found. No evidence of temporary or permanent inactivation was found with 28°g/ml solutions sheared in the presence of urea. Shear forces alone were not found to be as effective in causing enzyme inactivation as is generally believed and alternative mechanisms for damage are discussed.