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J. Biol. Chem., Vol. 279, Issue 50, 51908-51914, December 10, 2004

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Role of a Bacterial Organic Hydroperoxide Detoxification System in Preventing Catalase Inactivation^*

Ge Wang, Richard C. Conover, Stephane Benoit, Adriana A. Olczak, Jonathan W. Olson||, Michael K. Johnson, and Robert J. Maier¶

From the Departments of Microbiology and Chemistry, University of Georgia, Athens, Georgia 30602

In the gastric pathogen Helicobacter pylori, catalase (KatA) and alkyl hydroperoxide reductase (AhpC) are two highly abundant enzymes that are crucial for oxidative stress resistance and survival of the bacterium in the host. Here we report a connection unidentified previously between the two stress resistance enzymes. We observed that the catalase in ahpC mutant cells in comparison with the parent strain is inactivated partially (approximately 50%). The decrease of catalase activity is well correlated with the perturbation of the heme environment in catalase, as detected by electron paramagnetic resonance spectroscopy. To understand the reason for this catalase inactivation, we examined the inhibitory effects of hydroperoxides on H. pylori catalase (either present in cell extracts or added to the purified enzyme) by monitoring the enzyme activity and the EPR signal of catalase. H. pylori catalase is highly resistant to its own substrate, without the loss of enzyme activity by treatment with a molar ratio of 1:3000 H₂ O₂. However, it inactivated is by lower concentrations of organic hydroperoxides (the substrate of AhpC). Treatment with a molar ratio of 1:400 t-butyl hydroperoxide resulted in an inactivation of catalase by approximately 50%. UV-visible absorption spectra indicated that the catalase inactivation by organic hydroperoxides is caused by the formation of a catalytically incompetent compound II species. To further support the idea that organic hydroperoxides, which accumulate in the ahpC mutant cells, are responsible for the inactivation of catalase, we compared the level of lipid peroxidation found in ahpC mutant cells with that found in wild type cells. The results showed that the total amount of extractable lipid hydroperoxides in the ahpC mutant cells is approximately three times that in the wild type cells. Our findings reveal a novel role of the organic hydroperoxide detoxification system in preventing catalase inactivation.

Received for publication, July 26, 2004 , and in revised form, September 22, 2004.

^* This work was supported by National Institutes of Health Grants 1-RO1-DK60061 (to R. J. M.) and GM62542 (to M. K. J.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

^|| Present address: Dept. of Microbiology, North Carolina State University, Raleigh NC 27695.

^¶ To whom correspondence should be addressed: Microbiology Dept., University of Georgia, 805 Biology Science Bldg., Athens, GA 30602. Tel.: 706-542-2323; Fax: 706-542-6874; E-mail: rmaier{at}uga.edu.

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