catalases

Catalases are enzymes that catalyze the rapid decomposition of hydrogen peroxide into water and molecular oxygen. They are among the most efficient biological antioxidants, capable of processing large amounts of hydrogen peroxide. Most catalases are heme-containing enzymes that function as homotetramers, though other forms exist, including catalase-peroxidases (KatG) and manganese-containing catalases found in some organisms.

The canonical reaction is 2 H2O2 → 2 H2O + O2. The active site contains a heme iron. In the first step, hydrogen peroxide binds to the ferric heme and is reduced, forming water and a high-valent iron-oxo species known as Compound I. In the second step, a second molecule of hydrogen peroxide restores the enzyme to its resting ferric state while releasing water and oxygen. This two-step cycle enables rapid detoxification of hydrogen peroxide and distinguishes catalases from many peroxidases.

Diversity and localization: Typical monofunctional catalases are cytosolic or peroxisomal. In eukaryotes, peroxisomal catalase is common and contains a peroxisomal targeting signal for import. Bacteria often house cytosolic catalases. Some organisms possess Mn-containing catalases, which use a different metal center. Catalase-peroxidases (KatG) are bifunctional enzymes with both catalase and peroxidase activities and are notable in several bacteria, including pathogens.

Biological role: Catalases protect cells from oxidative damage by removing excess hydrogen peroxide produced during metabolism and photosynthesis. In humans, the CAT gene encodes catalase, which localizes primarily to peroxisomes and contributes to cellular redox homeostasis.

Applications: Catalases are used in laboratory and industrial settings to remove hydrogen peroxide from samples, in biotechnological processes, and in biosensing technologies.