Notes on Catalase for Biochemistry

by on January 30th, 2011
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Catalytic strategies: http://biology.kenyon.edu/BMB/Chime/catalase/frames/cattx.htm
serves to protect the cell from the toxic effects of hydrogen peroxide by catalyzing its decomposition into molecular oxygen and water without the production of free radicals.
http://web.archive.org/web/20000612104029/http://www.facstaff.bucknell.edu/toner/gb/lab121/labs34.html nonproteinaceous group, called the prosthetic group, that is important in the actual catalysis.
Regulation:
http://mic.sgmjournals.org/cgi/content/abstract/152/6/1671
MOA:
However, some enzymes that only have a single substrate do not fall into this category of mechanisms. Catalase is an example of this, as the enzyme reacts with a first molecule ofhydrogen peroxide substrate, becomes oxidised and is then reduced by a second molecule of substrate. Although a single substrate is involved, the existence of a modified enzyme intermediate means that the mechanism of catalase is actually a ping-pong mechanism, a type of mechanism that is discussed in the Multi-substrate reactions section below.
While complete mechanism of catalase is not currently known, the reaction is believed to occur in two stages: H2O2 + Fe(III)-E → H2O + O=Fe(IV)-E H2O2 + O=Fe(IV)-E → H2O + Fe(III)-E + O2[7] (where Fe()-E represents the iron centre of the heme group attached to the enzyme.) As hydrogen peroxide enters the active site it interacts with the amino acids Asn147 andHis74 , causing a proton (hydrogen ion ) to transfer between the oxygen atoms, polarizing and stretching the O-O bond, which breaks heterolytically. The free oxygen atom coordinates with the iron centre of the active site, freeing the newly formed water molecule and forming Fe(IV)=O. Next, the Fe(IV)=O reacts with a second hydrogen peroxide molecule to reform Fe(III)-E and produce water and oxygen.[7] The reactivity of the iron center may be improved by the presence of the phenolate ligand of Tyr357 in the fifth iron ligand , which can assist in the oxidation of the Fe(III) to Fe(IV). The efficiency of the reaction may also be improved by the interactions of His74 and Asn147 with reaction intermediates .[7] Generally, the rate of the reaction can be determined by the Michaelis-Menten equation .[4] Catalase can also oxidize different toxins, such as formaldehyde , formic acid , and alcohols . In doing so, it uses hydrogen peroxide according to the following reaction: H2O2 + H2R → 2H2O + R Again, the exact mechanism of this reaction is not known. Any heavy metal ion (such as Copper cations in Copper(II) sulfate ) will act as anoncompetitive inhibitor on catalase. Also, the poison cyanide is a competitive inhibitor of catalase, strongly binding to the heme of catalase and stopping the enzyme’s action. Three-dimensional protein structures of the peroxidated catalase intermediates are available at the Protein Data Bank . This enzyme is commonly used in laboratories as a tool for learning the effect of enzymes upon reaction rates.


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