Download Word Document: Catalase Fact Sheet

CATALASE Fact sheet
Activity and distribution
Although catalase has been intensively studied, its role in biological oxidation reactions is not known with
certainty. Since it is found in the microbodies of some cells (both plant and animal) it is believed to
catalyse the decomposition of hydrogen peroxide in those structures. Hydrogen peroxide is a poisonous
by-product of oxidative reactions in the cell, so catalase is classed as a peroxidase.
Reaction catalysed by catalase
H2O2 
H2O + ½O2
……………………..(1)
Question: How would you determine that catalase was found in the microbodies of plant or animal
cells? (Clue: You have to separate the microbodies from the rest of the cell.)
The role of catalase
Hydrogen peroxide is a poisonous compound and it must be broken down if it starts to build up in the
cell. The major source of hydrogen peroxide in the cell is from the oxidation of flavin-linked oxidases:
Reduced substrate
FADH
H202
Oxidised substrate
FAD
O2 ………….(2)
(FAD = Flavin Adenine Dinucleotide)
This takes place in the microbodies of plant and animal cells. So it is not surprising to find catalase
activity high in these cell organelles. Peroxysomes and glyoxysomes are microbodies found in the cells
of plants and. fungi, whilst similar microbodies are found in animal cells, especially in liver and kidney
tissues of mammals.
If FADH2 requires 1 mole of O2 per mole of FAD produced, as in (2) above,
And the subsequent reduction of hydrogen peroxide produces only ½ mole of O2, see equation (1).
Then there has been a net loss of half a mole of oxygen per mole of substrate oxidised.
Consequently, microbodies as well as mitochondria contribute to the overall respiratory gas
exchange of the cell.
“Nothing in biology makes sense except in the light of evolution” T. Dobzhansky
It is thought that the oxidation, seen in microbodies, represents an early attempt by primitive organisms to
protect themselves against the action of the poisonous gas oxygen when photosynthesis evolved and the
Earth’s atmosphere changed. Something like this is still seen today in the primitive anaerobic bacteria of
the Genus Clostridium. This bacterium is poisoned by the presence of free oxygen.
Some famous members of this Genus include Clostridium botulinum (which contaminates canned food
and causes the fatal food poisoning, botulism), and Clostridium tetani (whose spores are found in dust and
soil, it causes tetanus).
Marcel Zamocky (2008) Evolution of Catalases from Bacteria to Humans. Antioxid Redox Signal 10(9): 1527–1548
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2959186/
Structure of catalase
Catalase contains an iron cofactor bound in a prosthetic
heme group (like hemoglobin and the cytochromes)
Beef liver catalase
Cofactors of enzymes
Cofactors may be loosely bound so that:
ENZYME + COFACTOR =
HOLOENZYME (Active)
ENZYME - COFACTOR =
APOENZYME (Inactive)
Or they may be very tightly bound to the enzyme = a PROSTHETIC GROUP.
Bridging role bringing substrate and
enzyme together.
METAL ION ACTIVATORS
A catalyst itself, by being combined
with a protein it is enhanced.
COFACTORS
COENZYMES
Non-protein organic complexes
(e.g. certain vitamins)