The Open Door Web Site : IB Biology : Biochemistry : 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 and catalase is classed as a peroxidase.

Reaction catalysed by catalase



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:

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 makes sense in biology except in the light of evolution”

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 oxygenwhen 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).

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.