catalaseperoxidase

Catalase-peroxidase, commonly abbreviated KatG, is a large heme-containing enzyme found in certain bacteria. It is a bifunctional enzyme that exhibits both catalase activity, which decomposes hydrogen peroxide into water and oxygen, and peroxidase activity, which oxidizes a variety of substrates using hydrogen peroxide as oxidant.

KatG typically functions as a homodimer and contains a heme prosthetic group. The catalytic cycle involves the formation of reactive heme intermediates, such as Compound I, that mediate substrate oxidation, with a proximal histidine coordinating the heme and distant residues such as histidine and arginine shaping the reaction environment.

In pathogenic bacteria such as Mycobacterium tuberculosis, KatG plays a dual role. It contributes to oxidative stress defense and activates the antimycobacterial prodrug isoniazid (INH) by converting it to an active species that inhibits mycolic acid synthesis. As a result, katG mutations that disrupt prodrug activation while preserving catalase function can lead to isoniazid resistance; the S315T substitution is among the most common resistance-associated variants.

KatG homologs are found in diverse bacteria, particularly actinobacteria and some proteobacteria, reflecting its broad physiological relevance. Its dual activity and dependence on the heme cofactor make KatG a subject of study for understanding oxidative stress responses, drug activation, and enzyme evolution within the peroxidase-catalase family.