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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)