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Catalase

Catalase (human erythrocyte catalase: PDB 1DGF (http://www.rcsb.org/pdb/cgi/explore.cgi?pid=166031034358435&page=0&pdbId=1DGF), EC 1.11.1.6) is a common enzyme found in living organisms. Its functions include catalyzing the decomposition of hydrogen peroxide.

Hydrogen peroxide is formed as a waste product of metabolism in many living organisms. It is toxic and must be quickly converted into other, less dangerous, chemicals. To manage this problem, the enzyme catalase is frequently used to rapidly catalyse the decomposition of hydrogen peroxide into harmless oxygen and water. Catalase is mainly 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 - some lens cleaning systems sterilise the lenses by soaking them in a hydrogen peroxide solution, and catalase is used to decompose the peroxide before reinserting the lenses in the eye.

The complete mechanism of catalase is not yet known; however, the reaction occurs in two stages:

H2O2 + Fe(III)-E → H2O + O=Fe(IV)-E

H2O2 + O=Fe(IV)-E → H2O + Fe(III)-E

(Where Fe-E represents the iron centre of the heme group attached to the enzyme.)

As hydrogen peroxide enters the active site it is forced to interact with the amino acids His74 and Asn174. This causes a proton (hydrogen ion) to transfer from the first oxygen to the second, polarizing and stretching the O-O bond, which breaks heterolytically. The free oxygen atom coordinates with the iron centre of the active site, displacing the newly formed water molecule and forming Fe(IV)=O. In the second stage, the Fe(IV)=O reacts with another hydrogen peroxide to reform Fe(III)-E plus water and oxygen molecules.

3D Structures of the peroxidated catalase intermediates are available at the Protein Data Bank.

see also: peroxidases

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