Peroxisomes contain oxidative enzymes, such as catalase and uric acid oxidase . However the last enzyme is absent in humans, explaining the disease known as gout, caused by the accumulation of uric acid. Certain enzymes within the peroxisome, by using molecular oxygen, remove hydrogen atoms from specific organic substrates (labeled as R), in an oxidative reaction, producing hydrogen peroxide (H2O2, itself toxic):
RH2 + 02 --> R + H202
*Both catalase (breakdown of H202 into H20 and H) and oxidase (formation of H202 or H20) are present in peroxisomes.