An Alkyl Hydroperoxide Reductase from Salmonella typhimurium Involved in the Defense of DNA against Oxidative Damage

A peroxide reductase (peroxidase) which converts lipid hydroperoxides and other alkyl hydroperoxides to the corresponding alcohols, using either NADH or NADPH as the reducing agent, has been identified in both Salmonella typhimurium and Escherichia coli. This enzyme is shown to play a role in protecting against alkyl hydroperoxide mutagenesis. To our knowledge this work represents the first description of an NAD(P)H peroxidase in enteric bacteria and the first reported bacterial peroxidase to exhibit high activity toward alkyl hydroperoxides. A high performance liquid chromatography-based assay for the alkyl hydroperoxide reductase has been developed by monitoring the reduction of cumene hydroperoxide, a model alkyl hydroperoxide. By using this assay, the enzyme has been purified from a S. typhimurium regulatory mutant, oxyR1, which overexpresses a number of proteins involved in defenses against oxidative damage, and which contains 20-fold more of the alkyl hydroperoxide reductase than the wild-type strain. The purified activity requires the presence of two separable components having subunit molecular weights of 22,000 and 57,000. The 57-kDa protein contains a bound FAD cofactor and can use either NADH or NADPH as an electron donor for the direct reduction of redox dyes, or of alkyl hydroperoxides when combined with the 22-kDa protein. This enzyme may thus serve as a prokaryotic equivalent to the glutathione reductase/glutathione peroxidase system in eukaryotes.