[13] In 1937 catalase from beef liver was crystallized by James B. Sumner and Alexander Dounce[14] and the molecular weight was measured in 1938.

[17] While the complete mechanism of catalase is not currently known,[18] the reaction is believed to occur in two stages: Here Fe()-E represents the iron center of the heme group attached to the enzyme.

[19] Catalase can also catalyze the oxidation, by hydrogen peroxide, of various metabolites and toxins, including formaldehyde, formic acid, phenols, acetaldehyde and alcohols.

Hydrogen peroxide is a harmful byproduct of many normal metabolic processes; to prevent damage to cells and tissues, it must be quickly converted into other, less dangerous substances.

To this end, catalase is frequently used by cells to rapidly catalyze the decomposition of hydrogen peroxide into less-reactive gaseous oxygen and water molecules.

[25] However, catalase deficiency in mice may increase the likelihood of developing obesity, fatty liver,[26] and type 2 diabetes.

Catalase-positive pathogens, such as Mycobacterium tuberculosis, Legionella pneumophila, and Campylobacter jejuni, make catalase to deactivate the peroxide radicals, thus allowing them to survive unharmed within the host.

To activate the noxious spray, the beetle mixes the contents of the two compartments, causing oxygen to be liberated from hydrogen peroxide.

[38] Long-lived queens of the termite Reticulitermes speratus have significantly lower oxidative damage to their DNA than non-reproductive individuals (workers and soldiers).

[39] It appears that the efficient antioxidant capability of termite queens can partly explain how they attain longer life.

[42] Catalase is used in the food industry for removing hydrogen peroxide from milk prior to cheese production.

If the bacteria possess catalase (i.e., are catalase-positive), bubbles of oxygen are observed when a small amount of bacterial isolate is added to hydrogen peroxide.

The opposite end is then dipped into hydrogen peroxide, which is drawn into the tube through capillary action, and turned upside down, so that the bacterial sample points downwards.

The hand holding the tube is then tapped on the bench, moving the hydrogen peroxide down until it touches the bacteria.

The enzyme NADPH oxidase generates superoxide within the phagosome, which is converted via hydrogen peroxide to other oxidising substances like hypochlorous acid which kill phagocytosed pathogens.

[51] In individuals with chronic granulomatous disease (CGD), phagocytic peroxide production is impaired due to a defective NADPH oxidase system.

However, if individuals with CGD are infected with catalase-positive bacteria, the bacterial catalase can destroy the excess peroxide before it can be used to produce other oxidising substances.

Some catalase-positive bacteria and fungi include: Nocardia, Pseudomonas, Listeria, Aspergillus, Candida, E. coli, Staphylococcus, Serratia, B. cepacia and H.

Hydrogen peroxide can accumulate in hair follicles and if catalase levels decline, this buildup can cause oxidative stress and graying.

[57] Infection with the murine leukemia virus causes catalase activity to decline in the lungs, heart and kidneys of mice.

[63] Direct UV measurement of the decrease in the concentration of hydrogen peroxide is also widely used after the publications by Beers & Sizer[64] and Aebi.