MadSci Network: Biochemistry

Re: Why does catalase in chicken liver react so fast when NaOH is added(ph 10)?

Date: Mon Oct 18 22:25:13 1999
Posted By: Erin Cram, Grad student, Molecular and Cellular Biology, University of CA, Berkeley
Area of science: Biochemistry
ID: 939853227.Bc

Thanks for your question.

The precise answer to it is probably pretty complicated, because many things 
about a reaction change as the pH changes. I'll give it a shot, though, and 
give you some references for more information.

Catalase is an enzyme (a protein) composed of four identical units.    All 
proteins are made of amino acids, molecules which are sensitive to pH.  As 
pH changes, the amino acids can gain or lose hydrogens.  This affects the 
charge of the amino acid, and the resulting charge of the protein.  If the 
charge of a protein changes, the protein can change "conformation" or shape.  
In its new shape, it can have a harder (or easier) time interacting with 
other proteins, or with substrates. Also, each unit of catalase holds onto a 
structure called a "heme" group.  You may have heard of the "heme" in 
hemoglobin, the molecule that carries oxygen in the blood.  Heme groups are 
complicated structures that hold onto an iron molecule, a charged atom that 
can be used to provide the correct interactions for a chemical reaction.

Catalase binds to two H2O2 molecules at a time, and converts them to 2 
waters and molecular oxygen.  The kinetics, or how fast catalase can convert 
H2O2, changes with pH.  This could be because of changes in affinity for 
H2O2, or changes in the interactions of amino acids with the H2O2 that 
actually convert it to water and oxygen. 

Although I did find several articles that indicated that catalase was 
inhibited (less active) at acid pH, and one article that had maximum 
activity at a pH around pH 10, it is unusual for cells in the body to have 
such an alkaline pH.  Therefore, catalase also does work at lower pH.

Here are two articles about catalase:

LeHir etal Histochemistry Nov. 1979 64(1):51-66
Abe, K etal Journal of Biochemistry Feb. 1979 85(2):473-9

And two really good web sites:

Hope that is helpful.

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