Bifunctional enzyme with both catalase and broad-spectrum peroxidase activity. Also displays NADH oxidase, INH lyase and isonicotinoyl-NAD synthase activities. AH2 + H2O2 = A + 2 H2O 2 H2O2 = 2 H2O + O2 Binds 2 heme B (iron-protoporphyrin IX) groups per tetramer. Optimum pH is 4.25 for the peroxidase reaction and 7.5 for the catalase reaction. Homotetramer. By hydrogen peroxide. The N-terminus is blocked. Formation of the three residue Trp-Tyr-Met cross-link is important for the catalase, but not the peroxidase activity of the enzyme. Cells are more sensitive to killing by nalidixic acid, the effect is mitigated by pretreatment with 2,2'-bipyridyl and thiourea, both of which inhibit hydroxyl radical accumulation. Belongs to the peroxidase family. Peroxidase/catalase subfamily.