Bifunctional enzyme with both catalase and broad-spectrum peroxidase activity, oxidizing various electron donors including NADP(H) (By similarity). Protects M.tuberculosis against toxic reactive oxygen species (ROS) including hydrogen peroxide as well as organic peroxides and thus contributes to its survival within host macrophages by countering the phagocyte oxidative burst (PubMed:15165233). Also displays efficient peroxynitritase activity, which may help the bacterium to persist in macrophages (By similarity). Catalyzes the oxidative activation of the antitubercular pro-drug isoniazid (INH) to generate an isonicotinoyl radical that then reacts nonenzymatically with NAD to form an isonicotinoyl-NAD adduct which inhibits InhA. 2 H2O2 = 2 H2O + O2 AH2 + H2O2 = A + 2 H2O Binds 1 heme b (iron(II)-protoporphyrin IX) group per dimer. Homodimer. By the metal chelator phenanthroline via Rip1, RskA/SigK and RslA/SigL. Formation of the three residue Trp-Tyr-Met cross-link is important for the catalase, but not the peroxidase activity of the enzyme. Cells lacking this gene are devoid of catalase activity, supersensitive to H(2)O(2) exposure and highly resistant to the antitubercular drug isoniazid (INH) in vitro. This mutant strain is markedly attenuated for virulence in mice and displays impaired growth in infected macrophages, but its growth and survival is indistinguishable from wild-type in macrophages lacking the ROS-generating NADPH oxidase (Phox). Belongs to the peroxidase family. Peroxidase/catalase subfamily.