Catalase is a common enzyme found in nearly all living organisms exposed to oxygen.
It catalyzes the decomposition of hydrogen peroxide to water and oxygen.
It is a very important enzyme in protecting the cell from oxidative damage by reactive
oxygen species.
Likewise, catalase has one of the highest turnover numbers of all enzymes; one catalase
molecule can convert millions of molecules of hydrogen peroxide to water and oxygen each
second.
Catalase is a tetramer of four polypeptide chains, each over 500 amino acids long.
It contains four porphyrin heme groups that allow the enzyme to react with the hydrogen
peroxide.
The optimum pH for human catalase is approximately 7, and has a fairly broad maximum.
The pH optimum for other catalases varies between 4 and 11 depending on the species.
The optimum temperature also varies by species.
History Catalase was first noticed in 1818 when Louis
Jacques Thénard, who discovered H2O2, suggested its breakdown is 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.
In 1937 catalase from beef liver was crystallised by James B. Sumner and Alexander Dounce and
the molecular weight was found in 1938.
In 1969, the amino acid sequence of bovine catalase was discovered.
Then in 1981, the three-dimensional structure of the protein was revealed.
Action The reaction of catalase in the decomposition
of hydrogen peroxide in living tissue: 2 H2O2 → 2 H2O + O2
The presence of catalase in a microbial or tissue sample can be tested by adding a volume
of hydrogen peroxide and observing the reaction.
The formation of bubbles, oxygen, indicates a positive result.
This easy assay, which can be seen with the naked eye, without the aid of instruments,
is possible because catalase has a very high specific activity, which produces a detectable
response.
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 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 "supporting electrons" from the heme ligand.
This heme has to be drawn then as a radical cation.
As hydrogen peroxide enters the active site, it interacts with the amino acids Asn147 and
His74, causing a proton 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
Tyr357 in the fifth iron ligand, 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 His74 and
Asn147 with reaction intermediates.
In general, the rate of the reaction can be determined by the Michaelis-Menten equation.
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: H2O2 + H2R → 2H2O + R
The exact mechanism of this reaction is not known.
Any heavy metal ion sulfate) can act as a noncompetitive inhibitor of catalase.
Furthermore, the poison cyanide is a competitive inhibitor of catalase at high concentrations
of hydrogen peroxide.
Three-dimensional protein structures of the peroxidated catalase intermediates are available
at the Protein Data Bank.
This enzyme is commonly used in laboratories as a tool for learning the effect of enzymes
upon reaction rates.
Cellular role 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.
The true biological significance of catalase is not always straightforward to assess: Mice
genetically engineered to lack catalase are phenotypically normal, indicating this enzyme
is dispensable in animals under some conditions.
A catalase deficiency may increase the likelihood of developing type 2 diabetes.
Some humans have very low levels of catalase, yet show few ill effects.
The predominant scavengers of H2O2 in normal mammalian cells are likely peroxiredoxins
rather than catalase.
Human catalase works at an optimum temperature of 45°C,.
In contrast, catalase isolated from the hyperthermophile archaeon Pyrobaculum calidifontis has a temperature
optimum of 90°C. Catalase is usually located in a cellular,
bipolar environment organelle called the peroxisome.
Peroxisomes in plant cells are involved in photorespiration and symbiotic nitrogen fixation
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.
Catalase contributes to ethanol metabolism in the body after ingestion of alcohol, but
it only breaks down a small fraction of the alcohol in the body.
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 the bombardier beetle.
This 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 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 which rapidly heats the mixture to the boiling
point.
Catalase is also universal among plants, and many fungi are also high producers of the
enzyme.
Almost all aerobic microorganisms use catalase.
It is also present in some anaerobic microorganisms, such as Methanosarcina barkeri.
Applications
Catalase is used in the food industry for removing hydrogen peroxide from milk prior
to cheese production.
Another use is in food wrappers where it prevents food from oxidizing.
Catalase is also used in the textile industry, removing hydrogen peroxide from fabrics to
make sure the material is peroxide-free.
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.
Catalase test
The catalase test is also one of the main three tests used by microbiologists to identify
species of bacteria.
The presence of catalase enzyme in the test isolate is detected using hydrogen peroxide.
If the bacteria possess catalase, when a small amount of bacterial isolate is added to hydrogen
peroxide, bubbles of oxygen are observed.
The catalase 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 the mixture produces bubbles or froth, the organism is said to be 'catalase-positive'.
Staphylococci and Micrococci are catalase-positive.
Other catalase-positive organisms include Listeria, Corynebacterium diphtheriae, Burkholderia
cepacia, Nocardia, the family Enterobacteriaceae, Mycobacterium tuberculosis, Aspergillus, Cryptococcus,
and Rhodococcus equi.
If not, the organism is 'catalase-negative'.
Streptococcus and Enterococcus spp.
are catalase-negative.
While the catalase test alone cannot identify a particular organism, combined with other
tests, such as antibiotic resistance, it can aid identification.
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 amount of bacteria is collected on the end of the capillary tube.
The opposite end is then dipped into hydrogen peroxide which will draw up the liquid, and
turned upside down, so the bacterial end is closest to the bench.
A few taps of the arm should then move the hydrogen peroxide closer to the bacteria.
When the hydrogen peroxide and bacteria are touching, bubbles may begin to rise, giving
a positive catalase result.
Gray hair According to recent scientific studies, low
levels of catalase may play a role in the graying process of human hair.
Hydrogen peroxide is naturally produced by the body and catalase breaks it down.
If catalase levels decline, hydrogen peroxide cannot be broken down as well.
This allows the hydrogen peroxide to bleach the hair from the inside out.
This finding may someday be incorporated into cosmetic treatments for graying hair.
Interactions Catalase has been shown to interact with the
ABL2 and Abl genes.
See also Enzyme kinetics
Peroxidases Superoxide dismutase
References
External links "GenAge entry for CAT".
Human Ageing Genomic Resources.
Retrieved 2009-03-05.
"Catalase".
MadSci FAQ.
madsci.org.
Retrieved 2009-03-05.
"Catalase and oxidase test video".
Regnvm Prokaryotae.
Retrieved 2009-03-05.
"EC 1.11.1.6 - catalase".
Brenda: The Comprehensive Enzyme Information System.
Retrieved 2009-03-05.
"PeroxiBase - The peroxidase database".
Swiss Institute of Bioinformatics.
Retrieved 2009-03-05.
"Catalase Procedure".
MicrobeID.com.
Retrieved 2009-04-22.
"Catalase Molecule of the Month".
Protein Data Bank.
Retrieved 2013-01-08.