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Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals) which catalyst the decomposition of hydrogen peroxide to water and oxygen. It is a very important enzyme in protecting the cell from oxidative stress by reactive oxygen species (ROS). Catalase has one of the highest of all enzymes; one catalase molecule can convert millions of hydrogen peroxide molecules to water and oxygen each second.
Catalase is a tetramer of four polypeptide chains, each over 500 long. It contains four iron-containing heme groups that allow the enzyme to react with hydrogen peroxide. The optimum pH for human catalase is approximately 7, (2025). 9780470110171 ISBN 9780470110171 and has a fairly broad maximum: the rate of reaction does not change appreciably between pH 6.8 and 7.5. (1984). 9780121820053 ISBN 9780121820053 The pH optimum for other catalases varies between 4 and 11 depending on the species. The optimum temperature also varies by species.
The amino acid sequence of bovine catalase was determined in 1969, and the three-dimensional structure in 1981.
Here Fe()-E represents the iron center of the heme group attached to the enzyme. Fe(IV)-E(.+) is a mesomeric form of Fe(V)-E, meaning the iron is not completely oxidized to +V, but receives some stabilising electron density from the heme ligand, which is then shown as a radical cation (.+).
As hydrogen peroxide enters the active site, it does not interact with the Asn148 (asparagine at position 148) and histidine, causing a proton (hydrogen ion) to transfer between the oxygen atoms. The free oxygen atom coordinates, freeing the newly formed water molecule and Fe(IV)=O. Fe(IV)=O reacts with a second hydrogen peroxide molecule to reform Fe(III)-E and produce water and oxygen. The reactivity of the iron center may be improved by the presence of the phenolate ligand of tyrosine in the fifth coordination position, which can assist in the oxidation of the Fe(III) to Fe(IV). The efficiency of the reaction may also be improved by the interactions of His75 and Asn148 with reaction intermediates. The decomposition of hydrogen peroxide by catalase proceeds according to first-order kinetics, the rate being proportional to the hydrogen peroxide concentration. (1984). 9780121820053 ISBN 9780121820053
Catalase can also catalyze the oxidation, by hydrogen peroxide, of various metabolites and toxins, including formaldehyde, formic acid, phenols, acetaldehyde and alcohols. It does so according to the following reaction:
The exact mechanism of this reaction is not known.
Any heavy metal ion (such as copper cations in copper(II) sulfate) can act as a noncompetitive inhibitor of catalase. However, "Copper deficiency can lead to a reduction in catalase activity in tissues, such as heart and liver." Furthermore, the poison cyanide is a noncompetitive inhibitor of catalase at high concentrations of hydrogen peroxide. Arsenate acts as an Enzyme activator. Three-dimensional protein structures of the peroxidated catalase intermediates are available at the Protein Data Bank.
Mice genetically engineered to lack catalase are initially phenotypically normal. However, catalase deficiency in mice may increase the likelihood of developing obesity, fatty liver, and type 2 diabetes. Some humans have very low levels of catalase (acatalasia), yet show few ill effects.
The increased oxidative stress that occurs with ageing in mice is alleviated by gene expression of catalase. Over-expressing mice do not exhibit the age-associated loss of spermatozoon, testicle germ cell and seen in wild-type mice. Oxidative stress in wild-type mice ordinarily induces oxidative DNA damage (measured as 8-oxodG) in sperm with aging, but these damages are significantly reduced in aged catalase over-expressing mice. Furthermore, these over-expressing mice show no decrease in age-dependent number of pups per litter. Overexpression of catalase targeted to mitochondria extends the lifespan of mice.
In , catalase is usually located in a cellular organelle called the peroxisome. (2025). 9780815332183, Garland Science. ISBN 9780815332183 Peroxisomes in plant cells are involved in photorespiration (the use of oxygen and production of carbon dioxide) and symbiotic nitrogen fixation (the breaking apart of diatomic nitrogen (N2) to reactive nitrogen atoms). Hydrogen peroxide is used as a potent antimicrobial agent when cells are infected with a pathogen. 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.
Like alcohol dehydrogenase, catalase converts ethanol to acetaldehyde, but it is unlikely that this reaction is physiologically significant.
Almost all aerobic microorganisms use catalase. It is also present in some anaerobic microorganisms, such as Methanosarcina barkeri. Catalase is also universal among plants and occurs in most fungi.
One unique use of catalase occurs in the bombardier beetle. This beetle has two sets of liquids that are stored separately in two paired glands. The larger of the pair, the storage chamber or reservoir, contains and hydrogen peroxide, while the smaller, the reaction chamber, contains catalases and . To activate the noxious spray, the beetle mixes the contents of the two compartments, causing oxygen to be liberated from hydrogen peroxide. The oxygen oxidizes the hydroquinones and also acts as the propellant. The oxidation reaction is very exothermic (ΔH = −202.8 kJ/mol) and rapidly heats the mixture to the boiling point.
Long-lived queens of the termite Reticulitermes speratus have significantly lower DNA oxidation than non-reproductive individuals (workers and soldiers). Queens have more than two times higher catalase activity and seven times higher expression levels of the catalase gene RsCAT1 than workers. It appears that the efficient antioxidant capability of termite queens can partly explain how they attain longer life.
Catalase enzymes from various species have vastly differing optimum temperatures. animals typically have catalases with optimum temperatures in the range of 15-25 °C, while mammalian or avian catalases might have optimum temperatures above 35 °C, and catalases from plants vary depending on their growth habit. In contrast, catalase isolated from the hyperthermophile archaeon Pyrobaculum calidifontis has a temperature optimum of 90 °C.
A minor use is in contact lens hygiene – a few lens-cleaning products disinfection the lens using a hydrogen peroxide solution; a solution containing catalase is then used to decompose the hydrogen peroxide before the lens is used again.
While the catalase test alone cannot identify a particular organism, it can aid identification when combined with other tests such as antibiotic resistance. The presence of catalase in bacterial cells depends on both the growth condition and the medium used to grow the cells.
may also be used. A small sample of bacteria is collected on the end of the capillary tube, without blocking the tube, to avoid false negative results. 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. If bubbles form on contact, this indicates a positive catalase result. This test can detect catalase-positive bacteria at concentrations above about 105 cells/mL, and is simple to use.
Direct UV measurement of the decrease in the concentration of hydrogen peroxide is also widely used after the publications by Beers & Sizer and Aebi. (1984). 9780121820053, Academic Press. ISBN 9780121820053
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