ABSTRACTd-Amino acid oxidase (DAO) is a hydrogen peroxide-generating enzyme that uses ad-amino acid as a substrate. We hypothesized that DAO may protect against bacterial infection, because hydrogen peroxide is one of the most important molecules in the antibacterial defense systems in mammals. We show here that DAO suppressed the growth ofStaphylococcus aureusin a manner that depended on the concentration of DAO andd-amino acidin vitro. Addition of catalase abolished the bacteriostatic activity of DAO. Although DAO plusd-Ala showed less bactericidal activity, addition of myeloperoxidase (MPO) greatly enhanced the bactericidal activity of DAO. Furthermore, DAO was able to utilize bacterial lysate, which containsd-Ala derived from peptidoglycan; this could produce hydrogen peroxide with, in the presence of myeloperoxidase, formation of hypochlorous acid. This concerted reaction of DAO and MPO led to the bactericidal action.In vivoexperiments showed that DAO−/−(mutant) mice were more susceptible toS. aureusinfection than were DAO+/+(wild-type) mice. These results suggest that DAO, together with myeloperoxidase, may play an important role in antibacterial systems in mammals.
Characterisation of the pathogenic effects of the in vivo expression of an ALS-linked mutation in D-amino acid oxidase: Phenotype and loss of spinal cord motor neurons