Is involved in NO detoxification in an aerobic process, termed nitric oxide dioxygenase (NOD) reaction that utilizes O(2) and NAD(P)H to convert NO to nitrate, which protects the bacterium from various noxious nitrogen compounds. Therefore, plays a central role in the inducible response to nitrosative stress. In the presence of oxygen and NADH, FHP has NADH oxidase activity, which leads to the generation of superoxide and H(2)O(2), both in vitro and in vivo, and it has been suggested that FHP might act as an amplifier of superoxide stress. Under anaerobic conditions, FHP also exhibits nitric oxide reductase and FAD reductase activities. However, all these reactions are much lower than NOD activity. NADPH + 2 nitric oxide + 2 O2 = H(+) + NADP(+) + 2 nitrate NADH + 2 nitric oxide + 2 O2 = H(+) + NAD(+) + 2 nitrate Binds 1 FAD per subunit. Binds 1 heme b group per subunit. Monomer. Under oxygen-limited conditions. Consists of two distinct domains; an N-terminal heme-containing oxygen-binding domain and a C-terminal reductase domain with binding sites for FAD and NAD(P)H. No protein-heme interactions have been detected at the distal side of the heme molecule. FHP is able to bind phospholipids with high affinity. Belongs to the globin family. Two-domain flavohemoproteins subfamily. In the C-terminal section; belongs to the flavoprotein pyridine nucleotide cytochrome reductase family.