| Catalase | |||||||||
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| Identifiers | |||||||||
| Symbol | Catalase | ||||||||
| Pfam | PF00199 | ||||||||
| InterPro | IPR011614 | ||||||||
| PROSITE | PDOC00395 | ||||||||
| SCOP2 | 7cat /SCOPe /SUPFAM | ||||||||
| OPM superfamily | 370 | ||||||||
| OPM protein | 3e4w | ||||||||
| CDD | cd00328 | ||||||||
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| CAT | |||||||||||||||||||||||||||||||||||||||||||||||||||
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| Identifiers | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Aliases | CAT, catalase | ||||||||||||||||||||||||||||||||||||||||||||||||||
| External IDs | OMIM:115500;MGI:88271;HomoloGene:55514;GeneCards:CAT;OMA:CAT - orthologs | ||||||||||||||||||||||||||||||||||||||||||||||||||
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| Wikidata | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Catalase is a commonenzyme found in nearly all living organisms exposed to oxygen (such asbacteria, plants, and animals) whichcatalyzes the decomposition ofhydrogen peroxide towater andoxygen.[5] It is a very important enzyme in protecting the cell fromoxidative damage byreactive oxygen species (ROS). Catalase has one of the highestturnover numbers of all enzymes; one catalase molecule can convert millions of hydrogen peroxide molecules to water and oxygen each second.[6]
Catalase is atetramer of four polypeptide chains, each over 500amino acids long.[7] It contains four iron-containingheme groups that allow the enzyme to react with hydrogen peroxide. The optimumpH for human catalase is approximately 7,[8] and has a fairly broad maximum: the rate of reaction does not change appreciably between pH 6.8 and 7.5.[9] The pH optimum for other catalases varies between 4 and 11 depending on the species.[10] The optimum temperature also varies by species.[11]
Human catalase forms atetramer composed of foursubunits, each of which can be conceptually divided into four domains.[12] The extensive core of each subunit is generated by an eight-stranded antiparallelβ-barrel (β1-8), with nearest neighbor connectivity capped by β-barrel loops on one side and α9 loops on the other.[12] Ahelical domain at one face of the β-barrel is composed of four C-terminal helices (α16, α17, α18, and α19) and four helices derived from residues between β4 and β5 (α4, α5, α6, and α7).[12] Alternative splicing may result in different protein variants.
Catalase was first noticed in 1818 byLouis Jacques Thénard, who discoveredhydrogen peroxide (H2O2). Thénard suggested its breakdown was caused by an unknown substance. In 1900,Oscar Loew was the first to give it the name catalase, and found it in many plants and animals.[13] In 1937 catalase from beef liver was crystallized byJames B. Sumner andAlexander Dounce[14] and the molecular weight was measured in 1938.[15]
Theamino acid sequence ofbovine catalase was determined in 1969,[16] and the three-dimensional structure in 1981.[17]
While the complete mechanism of catalase is not currently known,[18] thereaction is believed to occur in two stages:
Here Fe()-E represents theiron center of theheme 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 theactive site, it does not interact with theamino acids Asn148 (asparagine at position 148) andHis75, causing aproton (hydrogenion) 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.[18] The reactivity of the iron center may be improved by the presence of the phenolateligand ofTyr358 in the fifth coordination position, which can assist in theoxidation of the Fe(III) to Fe(IV). The efficiency of the reaction may also be improved by the interactions of His75 and Asn148 withreaction intermediates.[18] The decomposition of hydrogen peroxide by catalase proceeds according to first-order kinetics, the rate being proportional to the hydrogen peroxide concentration.[19]
Catalase can also catalyze the oxidation, byhydrogen peroxide, of various metabolites and toxins, includingformaldehyde,formic acid,phenols,acetaldehyde andalcohols. 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 incopper(II) sulfate) can act as anoncompetitive inhibitor of catalase. However, "Copper deficiency can lead to a reduction in catalase activity in tissues, such as heart and liver."[20] Furthermore, the poisoncyanide is a noncompetitive inhibitor[21] of catalase at high concentrations ofhydrogen peroxide.[22]Arsenate acts as anactivator.[23] Three-dimensionalprotein structures of the peroxidated catalase intermediates are available at theProtein Data Bank.
Hydrogen peroxide is a harmful byproduct of many normalmetabolic 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 thedecomposition of hydrogen peroxide into less-reactivegaseousoxygen and water molecules.[24]
Mice genetically engineered to lack catalase are initially phenotypically normal.[25] However, catalase deficiency in mice may increase the likelihood of developingobesity, fatty liver,[26] andtype 2 diabetes.[27] Some humans have very low levels of catalase (acatalasia), yet show few ill effects.
The increasedoxidative stress that occurs withaging in mice is alleviated byover-expression of catalase.[28] Over-expressing mice do not exhibit the age-associated loss ofspermatozoa,testiculargerm andSertoli cells seen in wild-type mice. Oxidative stress inwild-type mice ordinarily induces oxidativeDNA damage (measured as8-oxodG) insperm with aging, but these damages are significantly reduced in aged catalase over-expressing mice.[28] 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.[29]
Ineukaryotes, catalase is usually located in a cellularorganelle called theperoxisome.[30] Peroxisomes in plant cells are involved inphotorespiration (the use of oxygen and production of carbon dioxide) and symbioticnitrogen fixation (the breaking apart ofdiatomicnitrogen (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 asMycobacterium tuberculosis,Legionella pneumophila, andCampylobacter jejuni, make catalase to deactivate the peroxide radicals, thus allowing them to survive unharmed within thehost.[31]
Likealcohol dehydrogenase, catalase converts ethanol to acetaldehyde, but it is unlikely that this reaction is physiologically significant.[32]
The large majority of known organisms use catalase in everyorgan, with particularly high concentrations occurring in theliver in mammals.[33] Catalase is found primarily inperoxisomes and thecytosol oferythrocytes (and sometimes inmitochondria[34])
Almost allaerobic microorganisms use catalase. It is also present in someanaerobicmicroorganisms, such asMethanosarcina barkeri.[35] Catalase is also universal amongplants and occurs in mostfungi.[36]
One unique use of catalase occurs in thebombardier 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, containshydroquinones and hydrogen peroxide, while the smaller, the reaction chamber, contains catalases andperoxidases. 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.[37] The oxidation reaction is veryexothermic (ΔH = −202.8 kJ/mol) and rapidly heats the mixture to the boiling point.[38]
Long-lived queens of thetermiteReticulitermes speratus have significantly loweroxidative damage to their DNA than non-reproductive individuals (workers and soldiers).[39] Queens have more than two times higher catalase activity and seven times higher expression levels of the catalase gene RsCAT1 than workers.[39] It appears that the efficientantioxidant capability of termite queens can partly explain how they attain longer life.
Catalase enzymes from various species have vastly differing optimum temperatures.Poikilothermic 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,[40][41] and catalases from plants vary depending on theirgrowth habit.[40] In contrast, catalase isolated from thehyperthermophilearchaeonPyrobaculum calidifontis has a temperature optimum of 90 °C.[42]
Catalase is used in the food industry for removinghydrogen peroxide frommilk prior tocheese production.[43] Another use is in food wrappers, where it prevents food fromoxidizing.[44] Catalase is also used in thetextile industry, removing hydrogen peroxide from fabrics to make sure the material is peroxide-free.[45]
A minor use is incontact lens hygiene – a few lens-cleaning productsdisinfect 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.[46]
The catalase test is one of the three main tests used by microbiologists to identify species of bacteria. If the bacteria possess catalase (i.e., are catalase-positive), bubbles of oxygen are observed when a small amount of bacterialisolate is added to hydrogen peroxide. The catalase test is done by placing a drop of hydrogen peroxide on amicroscope slide. An applicator stick is touched to the colony, and the tip is then smeared onto the hydrogen peroxide drop.
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.
Capillary tubes may also be used. A small sample of bacteria is collected on the end of the capillary tube, without blocking the tube, to avoidfalse negative results. The opposite end is then dipped into hydrogen peroxide, which is drawn into the tube throughcapillary 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,[50] and is simple to use.
Neutrophils and otherphagocytes use peroxide to kill bacteria. The enzymeNADPH oxidase generatessuperoxide within thephagosome, which is converted via hydrogen peroxide to other oxidising substances likehypochlorous acid which killphagocytosed pathogens.[51] In individuals withchronic granulomatous disease (CGD), phagocytic peroxide production is impaired due to a defective NADPH oxidase system. Normal cellular metabolism will still produce a small amount of peroxide and this peroxide can be used to produce hypochlorous acid to eradicate the bacterial infection. 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. In these individuals the pathogen survives and becomes a chronic infection. This chronic infection is typically surrounded by macrophages in an attempt to isolate the infection. This wall of macrophages surrounding a pathogen is called agranuloma. Many bacteria are catalase positive, but some are better catalase-producers than others. Some catalase-positive bacteria and fungi include:Nocardia,Pseudomonas,Listeria,Aspergillus,Candida,E. coli,Staphylococcus,Serratia,B. cepacia andH. pylori.[52]
Acatalasia is a condition caused by homozygous mutations in CAT, resulting in a lack of catalase. Symptoms are mild and include oral ulcers. A heterozygous CAT mutation results in lower, but still present catalase.[53]
Low levels of catalase may play a role in thegraying process of human hair. Hydrogen peroxide is naturally produced by the body and broken down by catalase. Hydrogen peroxide can accumulate in hair follicles and if catalase levels decline, this buildup can cause oxidative stress and graying.[54] These low levels of catalase are associated with old age. Hydrogen peroxide interferes with the production ofmelanin, the pigment that gives hair its color.[55][56]
Catalase has been shown tointeract with theABL2[57] andAbl genes.[57] Infection with themurine leukemia virus causes catalase activity to decline in the lungs, heart and kidneys of mice. Conversely, dietary fish oil increased catalase activity in the heart, and kidneys of mice.[58]
In 1870, Schoenn discovered a formation of yellow color from the interaction of hydrogen peroxide with molybdate;[59] then, from the middle of the 20th century, this reaction began to be used for colorimetric determination of unreacted hydrogen peroxide in the catalase activity assay.[60] The reaction became widely used after publications by Korolyuk et al. (1988)[61] and Goth (1991).[62] The first paper describes serum catalase assay with no buffer in the reaction medium; the latter describes the procedure based on phosphate buffer as a reaction medium. Since phosphate ion reacts with ammonium molybdate,[62] the use of MOPS buffer as a reaction medium is more appropriate.[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.[65]
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