Serves to protect the cell against DNA damage by alkyl hydroperoxides. It can use either NADH or NADPH as electron donor for direct reduction of redox dyes or of alkyl hydroperoxides when combined with the AhpC protein (By similarity). Binds 1 FAD per subunit. Homodimer. By oxidative stress and catechol, and very weakly by heat shock. Belongs to the class-II pyridine nucleotide-disulfide oxidoreductase family.