Bifunctional enzyme with both catalase and broad-spectrum peroxidase activity. May play a role in the intracellular survival of mycobacteria. AH2 + H2O2 = A + 2 H2O 2 H2O2 = 2 H2O + O2 Binds 2 heme B (iron-protoporphyrin IX) groups per tetramer. Homotetramer. Formation of the three residue Trp-Tyr-Met cross-link is important for the catalase, but not the peroxidase activity of the enzyme. Defects cause isoniazid (INH) resistance. Belongs to the peroxidase family. Peroxidase/catalase subfamily.