Which enzyme catalyzes the breakdown of hydrogen peroxide into water and oxygen?

• A. Peroxidase
• B. Oxidase
• C. Sucrase
• D. Catalase

Answer: (D)

Hydrogen peroxide is a harmful reactive oxygen species, and cells defend themselves by converting it into harmless water and oxygen. The enzyme that does this most efficiently is catalase, which catalyzes the reaction 2 H2O2 → 2 H2O + O2. This rapid breakdown helps protect cellular components from oxidative damage and is a hallmark of catalase activity. Peroxidase does use H2O2, but it typically oxidizes other substrates rather than releasing oxygen gas. Sucrase acts on sucrose, not on hydrogen peroxide. Oxidase transfers electrons to oxygen in various oxidation reactions and often generates hydrogen peroxide as a byproduct rather than decomposing it into water and oxygen.