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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 X 10(7) M-1 X 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.
Insights
A mutant Proteus mirabilis catalase exhibits enhanced efficiency and stability against hydrogen peroxide compared to the wild-type enzyme. This purified catalase demonstrates higher specific activity and heat resistance, suggesting improved performance.
Area of Science:
- Biochemistry
- Enzymology
- Microbiology
Background:
- Catalase (EC 1.11.1.6) is crucial for detoxifying hydrogen peroxide.
- Proteus mirabilis PR is a mutant strain exhibiting strong resistance to hydrogen peroxide.
- Understanding catalase variations can reveal mechanisms of oxidative stress resistance.
Purpose of the Study:
- To purify and characterize catalase from a hydrogen peroxide-resistant Proteus mirabilis mutant (PR).
- To compare the properties of the mutant catalase with the wild-type enzyme.
- To investigate the enhanced resistance and efficiency of the mutant catalase.
Main Methods:
- Purification of catalase from P. mirabilis PR to homogeneity.
- Ion-exchange chromatography to resolve catalase forms (A and B).
- Comparison of purified mutant catalase with wild-type enzyme using biochemical assays, molecular weight determination, subunit analysis, isoelectric focusing, and antibody reactivity.
Main Results:
- Catalase from the mutant PR existed as two forms (A and B) in crude extracts, with form B transforming into form A.
- Pure catalase from the mutant (form A) showed higher specific activity (2.7 X 10^7 M^-1 s^-1) and purity index (1.12) than previously reported for wild-type.
- The mutant catalase exhibited increased heat stability and resistance to 3-amino-1,2,4-triazole compared to beef liver catalase.
Conclusions:
- The purified catalase (form A) from P. mirabilis PR is distinct from the wild-type enzyme.
- The mutant catalase is a more efficient and stable enzyme for hydrogen peroxide detoxification.
- Both P. mirabilis catalases display significant resistance to a common inhibitor, suggesting unique structural or functional adaptations.