What enzyme breaks down hydrogen peroxide in cells?

Catalase is the enzyme that breaks down hydrogen peroxide in cells. It converts hydrogen peroxide into water and oxygen, helping protect cells from oxidative damage caused by reactive oxygen species.

Hydrogen peroxide is produced naturally during metabolism, but it can damage proteins, membranes, and DNA if it accumulates. Catalase is especially abundant in peroxisomes and in red blood cells. Its active site contains a heme group with iron, which helps drive the reaction.

Catalase is exceptionally fast: one molecule can process millions of hydrogen peroxide molecules per second. The enzyme was first noticed in 1818, after Louis Jacques Thénard discovered hydrogen peroxide; Oscar Loew gave it the name catalase in 1900.

A common mix-up is confusing catalase with peroxidase. Both can act on hydrogen peroxide, but catalase characteristically decomposes two hydrogen peroxide molecules directly into water and oxygen. Microbiologists also use the catalase test: bubbling after hydrogen peroxide is added indicates a catalase-positive microorganism.