Properties of a catalase from a peroxide-resistant mutant of Proteus mirabilis

Abstract

A catalase (EC 1.11.1.6) from Proteus mirabilis PR, a mutant with strong resistance to hydrogen peroxide, was purified to homogeneity and compared with catalase from wild-type P. mirabilis. In crude extracts from the mutant, catalase was present as two different entities called A and B, that could be resolved by ion-exchange chromatography. The B form was transformed into A. The pure catalase preparation contained the A form only. This catalase was not found to be different from the wild-type enzyme, considering its molecular weight, subunit composition, isoelectric pH, and reactivity to specific antibodies. Partial proteolytic cleavage of the two bacterial enzymes with four different proteases proceeded at the same rate and produced identical patterns. However, pure catalase from the mutant had a specific activity against H2O2 of 2.7 × 107M−1∙s−1, and its purity index (A406/A280) was 1.12. These values were higher than previously determined for the wild-type enzyme. Furthermore, the mutant catalase was more stable to heat. The results suggest that the purified catalase (A form) differs from the wild-type enzyme and appears to be a more efficient catalase against H2O2. Both enzymes were found to be much more resistant than beef liver catalase to the classically used catalase inhibitor 3-amino-1,2,4-triazole.