AskDefine | Define catalase

Dictionary Definition

catalase n : enzyme found in most plant and animal cells that functions as an oxidative catalyst; decomposes hydrogen peroxide into hydrogen and water

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English

Noun

  1. An enzyme found in the liver that catalyses the decomposition of hydrogen peroxide to water and oxygen.

Extensive Definition

Catalase is a common enzyme found in nearly all living organisms. Its functions include catalyzing the decomposition of hydrogen peroxide to water and oxygen. Catalase has one of the highest turnover rates of all enzymes; one molecule of catalase can convert millions of molecules of hydrogen peroxide to water and oxygen per second.
Catalase is a tetramer of four polypeptide chains, each over 500 amino acids long. It contains four porphyrin heme (iron) groups that allow the enzyme to react with the hydrogen peroxide. The optimum pH for catalase is approximately (pH 7.0), while the optimum temperature varies by species.

History

Catalase was first noticed as a substance in 1811 when Louis Jacques Thénard, who discovered H2O2 (hydrogen peroxide), suggested that its breakdown is caused by a substance.
In 1900 Oscar Loew was the first to give it the name catalase, and found its presence in many plants and animals. In 1937 catalase from beef liver was crystallised by James B. Sumner and the molecular weight worked out in 1938. In 1969 the amino acid sequence of bovine catalase was worked out. Then in 1981, the 3D structure of the protein was revealed.

Action of catalase

The reaction of catalase in the decomposition of hydrogen peroxide is:
2 H2O2 → 2 H2O + O2
In microbiology, the catalase test is used to differentiate between bacterial species in the lab.http://www2.austin.cc.tx.us/microbugz/html/catalase_test.html The test is done by placing a drop of hydrogen peroxide on a microscope slide. Using an applicator stick, a scientist touches the colony and then smears a sample into the hydrogen peroxide drop. If bubbles or froth forms, the organism is said to be catalase-positive; if not, the organism is catalase-negative.http://dentistry.ouhsc.edu/intranet-web/courses/dmi_8351/Catalase.html This test is particularly useful in distinguishing staphylococci and micrococci, which are catalase-positive, from streptococci and enterococci, which are catalase-negative.http://www2.austin.cc.tx.us/microbugz/html/catalase_test.html While the catalase test alone cannot identify a particular organism, combined with other tests, it can aid diagnosis. The presence of catalase in bacterial cells depends on both the growth condition and the medium used to grow the cells.

Molecular mechanism

While the complete mechanism of catalase is not currently known, the reaction is believed to occur in two stages:
H2O2 + Fe(III)-E → H2O + O=Fe(IV)-E(.+)
H2O2 + O=Fe(IV)-E(.+) → H2O + Fe(III)-E + O2
Here Fe()-E represents the iron centre of the heme group attached to the enzyme. Fe(IV)-E(.+) ís a mesomeric form of Fe(V)-E, meaning that iron is not completely oxidized to +V but receives some "supporting electron" from the heme ligand. This heme has to be drawn then als radical cation (.+).
As hydrogen peroxide enters the active site, it interacts with the amino acids Asn147 (asparagine at position 147) and His74, 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 true biological significance of catalase is not always straightforward to assess: Mice genetically engineered to lack catalase are phenotypically normal, indicating that this enzyme is dispensable in animals under some conditions.
Some human beings have very low levels of catalase (acatalesimia), yet show few ill effects. It is likely that the predominant scavengers of H2O2 in normal mammalian cells are preoxiredoxins rather than catalase.
Catalase works at an optimum temperature of 37 °C, which is approximately the temperature of the human body.
Catalase is usually located in a cellular organelle called the peroxisome. 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. Pathogens that are catalase-positive, such as Mycobacterium tuberculosis, Legionella pneumophila, and Campylobacter jejuni, make catalase in order to deactivate the peroxide radicals, thus allowing them to survive unharmed within the host .http://mic.sgmjournals.org/cgi/content/full/149/9/2635

Distribution among organisms

All known animals use catalase in every organ, with particularly high concentrations occurring in the liver. One unique use of catalase occurs in bombardier beetle. The beetle has two sets of chemicals ordinarily stored separately in its paired glands. The larger of the pair, the storage chamber or reservoir, contains hydroquinones and hydrogen peroxide, whereas the smaller of the pair, the reaction chamber, contains catalases and peroxidases. To activate the 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.
Catalase is also universal among plants, but not among fungi, although some species have been found to produce the enzyme when growing in an environment with a low pH and warm temperatures.
Very few aerobic microorganisms are known that do not use catalase. http://madsci.org/posts/archives/jun99/929507203.Gb.r.html. Streptococcus species are an example of aerobic bacteria that do not possess catalase. Catalase has also been observed in some anaerobic microorganisms, such as Methanosarcina barkeri.

Human applications

Catalase is used in the food industry for removing hydrogen peroxide from milk prior to cheese production.http://www.worthington-biochem.com/CTL/default.html Another use is in food wrappers, where it prevents food from oxidizing.http://madsci.org/posts/archives/mar99/921636249.Gb.r.html Catalase is also used in the textile industry, removing hydrogen peroxide from fabrics to make sure the material is peroxide-free.http://www.p2pays.org/ref/11/10842.htm A minor use is in contact lens hygiene - a few lens-cleaning products disinfect 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. Recently, catalase has also begun to be used in the aesthetics industry. Several mask treatments combine the enzyme with hydrogen peroxide on the face with the intent of increasing cellular oxygenation in the upper layers of the epidermis.
The catalase test is also one of the main three tests used by microbiolgists to identify species of bacteria. The presence of catalase enzyme in the test isolate is detected using hydrogen peroxide. This when exposed to a small amount of a bacterial isolate will bubble if the bacteria posess this enzyme.

Pathology

The peroxisomal disorder acatalasia is due to a deficiency in the function of catalase.
catalase in Arabic: كتالاز
catalase in Catalan: Catalasa
catalase in Czech: Kataláza
catalase in German: Katalase
catalase in Spanish: Catalasa
catalase in Basque: Katalasa
catalase in French: Catalase
catalase in Italian: Catalasi
catalase in Dutch: Katalase
catalase in Japanese: カタラーゼ
catalase in Polish: Katalaza
catalase in Portuguese: Catalase
catalase in Russian: Каталаза
catalase in Slovenian: Katalaza
catalase in Serbian: Каталаза
catalase in Swedish: Katalas
catalase in Ukrainian: Каталаза
catalase in Chinese: 过氧化氢酶
for systematic sequence analysis of catalases AND peroxidases see http://peroxibase.isb-sib.ch/
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