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CATALASE
OANA NAFORNITA & WENDELA BIRGERSSON
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 reproductive
reactions and 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 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
Catalase was first noticed in
1811 when Louis Jacques
Thénard, who discovered
hydrogen peroxide, 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 1969, the amino acid sequence of bovine
catalase was worked out. Then in 1981, the threedimensional structure of the protein was revealed.
PRIMARY STRUCTURE
The primary
structure of catalase
consists of a
polypeptide chain
made up of 506
amino acids, one
heme group and one
NADH molecule.
SECONDARY STRUCTURE
Only about 60% of catalase structure is composed
of regular secondary structural motifs: a-helices
account for 26% of its structure and b-structure
for 12%. Irregular structure includes a
predominance of extended single stands and loops
that play a major role in the assembly of the
tetramer.
TERTIARY STRUCTURE
The tertiary structure is globular and is held
together with disulphide bridges and hydrogen
bonds. This globular structure is the one which
makes catalase soluble in water.
QUATERNARY STRUCTURE
The quaternary structure
comprises four monomer
sub-units. Each monomer
has a porphyrin heme
group and a NADPH
molecule. Porphyrin
is made up of a
photoporphyrin ring and
central iron (Fe) atom.
RELATION BETWEEN STRUCTURE AND FUNCTION
An increase in the concentration of substrate would cause
an increase in the rate of catalase activity because of a
larger chance that catalase enzymes will collide with
hydrogen peroxide molecules and the active site reacting
with the hydrogen peroxide.
The rate of reaction doubles as the concentration of
hydrogen peroxide doubles because there are twice the
number of substrate molecules so the active sites are twice
as likely to collide with a substrate molecule.
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
treatments for graying hair