Bifunctional enzyme with both catalase and broad-spectrum peroxidase activity. Also displays NADH oxidase, isoniazid hydrazine lyase and isonicotinoyl-NAD synthase activities. AH2 + H2O2 = A + 2 H2O 2 H2O2 = 2 H2O + O2 Binds 1 heme b (iron(II)-protoporphyrin IX) group per subunit. Optimum pH is 4.5 for the peroxidase reaction, 6.0 for the catalase reaction, and 8.75 for the NADH oxidase reaction. Homodimer. Formation of the three residue Trp-Tyr-Met cross-link is important for the catalase, but not the peroxidase activity of the enzyme. Belongs to the peroxidase family. Peroxidase/catalase subfamily.