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Abstract
Reactive oxygen species (ROS) such as hypochlorous acid (HOCl) and hydrogen peroxide (H2O2) selectively oxidize amino acid residues in proteins leading to loss of enzymatic activity. Helicobacter pylori (H. pylori), a microaerophilic bacterium involved in the cause of stomach ulcers, has a unique ability to survive under high levels of oxidative stress. Catalase of H. pylori plays a major role in defense from oxidative stress naturally occurring in the human body. The loss of catalase activity due to oxidative damage renders the bacterium more vulnerable to further damage. To protect itself from oxidative stress, the H. pylori bacterium produces an enzyme called methionine sulfoxide reductase (Msr), which reductively repairs methionine sulfoxide to its native form. Since methionine residues of pathogens are the major targets of oxidation, the Msr targets only the damaged methionines caused by oxidative stress. With the help of mass spectrometry, identification and quantification of specific methionines being repaired in H. pylori catalase was determined by comparing the percent of oxidation of each methionine residue.