Catalyzes the oxidation of F420H(2) with O(2) (PubMed:15340796, PubMed:16218963). May be involved in O(2) detoxification, reducing the intracellular O(2) concentration to a level allowing growth at the expense of methane formation (PubMed:15340796). O2 + 2 reduced coenzyme F420-(gamma-L-Glu)(n) = 2 H(+) + 2 H2O + 2 oxidized coenzyme F420-(gamma-L-Glu)(n) Binds 1 FMN per subunit. Binds 2 iron ions per subunit. Optimum pH is near 7.5. Homodimer (PubMed:7649162). Homotetramer (PubMed:7730275, PubMed:17480207). The tetramer is composed of two functional dimers (PubMed:17480207). By iron limitation. Contains an N-terminal beta-lactamase-like domain harboring a di-iron center, and a C-terminal flavodoxin-like domain containing FMN. Two monomers assemble via a head-to-tail arrangement, such that the beta-lactamase and the flavodoxin domains face each other, thereby forming two separated and presumably independent active sites. In the N-terminal section; belongs to the zinc metallo-hydrolase group 3 family.