Catalase

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Catalase is a common enzyme found in almost all living organisms exposed to oxygen (such as bacteria, plants, and animals). It catalyzes the decomposition of hydrogen peroxide into water and oxygen. This is a very important enzyme in protecting cells from oxidative damage by reactive oxygen species (ROS). Likewise, catalase has one of the highest turnover rates of all enzymes; a single catalase molecule can convert millions of hydrogen peroxide molecules into water and oxygen every second.

Catalase is a tetramer of four polypeptide chains, each of which over 500 long amino acids. It contains four groups of iron-containing hems that allow the enzyme to react with hydrogen peroxide. The optimum pH for human catalase is about 7, and has a fairly large maximum: the reaction rate does not change significantly between pH 6.8 and 7.5. The optimum PH for the other catalase varies between 4 and 11 depending on the species. The optimum temperature also varies by species.

Video Catalase

Structure

Human catalase forms tetramer consisting of four subunits, each of which can be divided into four domains conceptually. The broad core of each subunit is produced by the eight-stranded antiparallel b-barrel (b1-8), with adjacent neighboring connectivity limited by the b-barrel loop on one side and the a9 loop on the other. A helical domain on a b-barrel face consists of four C-terminal helices (a16, a17, a18, and a19) and four helices derived from residues between b4 and b5 (a4, a5, a6, and a7). Alternate grafting can produce different protein variations.

Maps Catalase

History

Catalase was not noticed until 1818 when Louis Jacques ThÃÆ' nà © nard, who discovered H ₂ O ₂ (hydrogen peroxide), suggested the solution was caused by an unknown substance. In 1900, Oscar Loew was the first to name it catalase, and found it in many plants and animals. In 1937 the catalase of the liver of the cow was crystallized by James B. Sumner and Alexander Dounce and molecular weight was discovered in 1938.

The sequence of amino acids from bovine catalase was determined in 1969, and the three-dimensional structure in 1981.

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Function

Action

Catalase catalyzes the following reactions:

2 H ₂ O ₂ -> 2 H ₂ O O ₂

The presence of catalase in microbial or tissue samples can be demonstrated by adding hydrogen peroxide and observing the reaction. Oxygen production can be seen by bubble formation. This easy test, which can be seen with the naked eye, without the aid of an instrument, is possible because the catalase has a very high specific activity, resulting in a detectable response, and the fact that one of its products is gas.

Molecular mechanism

While the complete mechanism of catalase is currently unknown, the reaction is believed to occur in two stages: <(sub> 2 OO = Fe (IV) -E (<.) <= sub> 2 O ₂ O = Fe (IV) -E (.) -> H ₂ O Fe (III) -EO ₂

Here Fe () - E represents the iron center of the heme group attached to the enzyme. Fe (IV) -E (.) Is the mesomeric form of Fe (V) -E, which means iron is not fully oxidized to V but receives some stable electron density from the heme ligand, which is then represented as radical cation (.

When hydrogen peroxide enters the active site, hydrogen interacts with the amino acid Asn148 (asparagin at position 148) and His75, causing protons (hydrogen ions) to move between oxygen atoms. Oxygen free oxygen coordinates free the newly formed water molecules and Fe (IV) = O. Fe (IV) = O reacts with the second hydrogen peroxide molecule to reform Fe (III) -E and produce water and oxygen. The reactivity of the iron center can be increased by the presence of a phenolic ligand from Tyr358 in the fifth coordinate position, which may be helpful in Fe (III) oxidation to Fe (IV). The efficiency of the reaction can also be enhanced by the interactions of His75 and Asn148 with reaction intermediates. In general, the rate of the reaction can be determined by the Michaelis-Menten equation.

Catalase can also catalyze oxidation, by hydrogen peroxide, various metabolites and toxins, including formaldehyde, formic acid, phenol, acetaldehyde and alcohols. It does so in accordance with the following reaction: 2 R -> 2H ₂ O R 2

The exact mechanism of this reaction is unknown.

All heavy metal ions (such as copper cations in copper (II) sulfate) may act as an uncompetitive catalase inhibitor. Further, the cyanide poison is a [[noncompetitive inhibitor]] of the catalase at high concentrations of hydrogen peroxide. Arsenate acts as an activator. The three-dimensional protein structure of the triggered peroxidation intermediates is available in Protein Data Bank.

Mobile role

Hydrogen peroxide is a dangerous by-product of many normal metabolic processes; to prevent cell and tissue damage, it must be quickly converted into other less harmful substances. For this purpose, catalase is often used by cells to catalyze the decomposition of hydrogen peroxide into gas molecules and less reactive water molecules.

Mice genetically engineered for catalase deficiency are initially phenotypic, but catalase deficiency in rats may increase the likelihood of developing obesity, fatty liver, and type 2 diabetes. Some humans have very low catalase levels (acatalasia), but show some adverse effects.

Increased oxidative stress that occurs with aging in rats is reduced by the excessive expression of catalase. Overly expressing mice did not show the loss of spermatozoa, testicular bacteria and age-related Sertoli cells seen in wild-type mice. Oxidative stress in wild-type rats usually induces oxidative DNA damage (measured as 8-oxodg) in sperm with aging, but this damage is significantly reduced in older, over-expressing mice. Furthermore, these excessive expressing rats do not show a decrease in the number of puppies depending on age per litter. The excessive expression of the catalase targeted to the mitochondria extends the life of the mice.

Catalase is usually located in a cellular organ called peroxisomes. Peroxisomes in plant cells are involved in photorespiration (use of oxygen and carbon dioxide production) and symbiotic nitrogen fixation (diatomic nitrogen separation (N ₂ ) into reactive nitrogen atoms). Hydrogen peroxide is used as a potent antimicrobial agent when cells are infected with pathogens. Positive pathogenic pathogens, such as Mycobacterium tuberculosis < Legionella pneumophila , and Campylobacter jejuni , make catalase to deactivate peroxide radicals, allowing them to survive without injury in the host.

Like alcohol dehydrogenase, catalase converts ethanol into acetaldehyde, but it is unlikely that this reaction is physiologically significant.

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Distribution between organisms

Most of the known organisms use catalase in every organ, with very high concentrations occurring in the liver in mammals. One unique use of catalase occurs in bomber beetles. This beetle has two sets of fluids stored separately in two paired glands. The larger the couple, the storage space or reservoir, contain hydroquinone and hydrogen peroxide, while the smaller, reaction chamber contains catalase and peroxidase. To activate the dangerous spray, the beetle mixes the contents of the two compartments, causing oxygen to be released from hydrogen peroxide. Oxygen oxidizes hydroquinone and also acts as a propellant. The oxidation reaction is very exothermic (? H = -202.8 kJ/mol) and rapidly heats the mixture to the boiling point.

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.

The long-term queen of termites Reticulitermes speratus significantly decreases oxidative damage to their DNA rather than non-reproductive individuals (workers and soldiers). Queens has more than twice the catalase activity and the catalase level of the RsCAT1 catalase gene is seven times higher than that of workers. It seems that the efficient antioxidant ability of termite queens can partly explain how they reach longer lives.

The enzyme catalase of various species has very different optimum temperatures. Poicillotermic animals typically have catalase with optimum temperatures in the range of 15-25 Â ° C, whereas mammals or poultry can have optimum temperatures above 35 Â ° C, and catalase from plants varies depending on their growth habits. In contrast, the catalase isolated from hypertermophile archaeon Pyrobaculum calidifontis has an optimum temperature of 90Ã, Â ° C.

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Significance and clinical applications

Catalase is used in the food industry to remove hydrogen peroxide from milk before cheese production. Another use is in food wrappers that prevent food from oxidizing. Catalase is also used in the textile industry, removing hydrogen peroxide from the fabric to ensure its peroxide free material.

Small use in the hygiene of contact lenses - some lens cleaning products disinfect the lens using a hydrogen peroxide solution; a solution containing catalase is then used to decompose hydrogen peroxide before the lens is used again.

Identification of bacteria (catalase test)

The catalase test is one of three major tests used by microbiologists to identify bacterial species. If the bacteria have catalase (ie, catalase-positive), when a small amount of bacterial isolate is added to hydrogen peroxide, oxygen bubbles are observed. The catalase test is performed by placing a drop of hydrogen peroxide on a microscope slide. The applicator's wand is touched to the colony, and the tip is then applied to a droplet of hydrogen peroxide.

• If the mixture produces bubbles or foam, the organism is said to be 'catalase-positive'. Staphylococci and Micrococci are positive catalases. Other catalase-positive organisms include Listeria, Corynebacterium diphtheriae, Burkholderia cepacia, Nocardia , Enterobacteriaceae family ( Citrobacter, E. coli, Enterobacter, Klebsiella, Shigella, Yersinia, Proteus, Salmonella, Serratia ), Pseudomonas, Mycobacterium tuberculosis, Aspergillus , Cryptococcus , and Rhodococcus equi .
• Otherwise, the organism is 'catalase-negative'. Streptococcus and Enterococcus spp. is catalase-negative.

While the catalase test alone can not identify a particular organism, it can aid in identification when combined with other tests such as antibiotic resistance. The presence of catalase in bacterial cells depends on growth conditions and the media used to grow cells.

Capillary tubes can also be used. Small samples of bacteria are collected at 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 pulled into the tube through capillary action, and reversed, so that the bacterial points down. The hand holding the tube then tapped the bench, moving the hydrogen peroxide down until it touched the bacteria. If a bubble is formed on contact, this indicates a positive catalase result. This test can detect positive catalase bacteria at concentrations above about 10 ⁵ cells/mL, and is easy to use.

Virulence of bacteria

Neutrophils and other phagocytes use peroxides to kill bacteria. NADPH oxidase enzyme produces superoxide in phagosomes, which are converted through hydrogen peroxide to other oxidizing agents such as hypochlorite acid that kills phagocytic pathogens. In individuals with chronic granulomatous disease (CGD) there are defects in producing peroxide through mutations in phagocyte oxidation such as myeloperoxidase. Normal cellular metabolism will still produce a small amount of peroxide and these peroxides can be used to produce hypochlorite acid to eradicate bacterial infections. However, if individuals with CGD are infected with positive catalase bacteria, the bacterial catalase can destroy the excess peroxide before it can be used to produce other oxidizing agents. In these individuals the pathogen survives and becomes a chronic infection. This chronic infection is usually surrounded by macrophages in an effort to isolate the infection. The macrophage wall that surrounds this pathogen is called granuloma. Many bacteria are positive catalases, but some are better catalase manufacturers than others. "Mnemonic" Cat Need PLACESS to Belch Hairballs "can be used to memorize positive catalase bacteria: nocardia, pseudomonas, listeria, aspergillus, candida, E. coli, staphylococcus, serratia, B. cepacia and H. pylori.

Gray hair

Low levels of catalase can play a role in the process of human hair gray hair. Hydrogen peroxide is naturally produced by the body and broken down by catalase. If the catalase level decreases, hydrogen peroxide can not be broken down properly. Hydrogen peroxide interferes with the production of melanin, the pigment that gives color to the hair.

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Interactions

Catalase has been shown to interact with the ABL2 and Abl genes. Infections with the murine leukemia virus cause decreased catalase activity in the lungs, heart and kidney mice. In contrast, fish oil foods increase catalase activity in the heart, and kidney mice.

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See also

• enzyme kinetics
• Glutathione peroxidase
• Peroxidase
• Superoxide dismutase

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References

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External links

• "GenAge entry for CAT (Homo sapiens)". Human Genome Resource Aging . Retrieved 2009-03-05 .
• "Catalase". FAQ MadSci . madsci.org . Retrieved 2009-03-05 .
• "Video of catalase and oxidase test". Regnvm Prokaryotae . Retrieved 2009-03-05 .
• "EC 1.11.1.6 - catalase". Brenda: Comprehensive Enzyme Information System . Retrieved 2009-03-05 .
• "PeroxiBase - Peroxidase database". Institute of Bioinformatics Switzerland. Archived from the original in 2008-10-13 . Retrieved 2009-03-05 .
• "Catalysis Procedure". MicrobeID.com . Retrieved 2009-04-22 .
• "Molecular Catalysis of the Month". Protein Data Bank. Archived from the original in 2013-05-11 . Retrieved 2013-01-08 .

Source of the article : Wikipedia