MadSci Network: Biochemistry
Query:

Re: how does Cu2+ inhibit the action of catalase?

Date: Fri Apr 6 14:00:42 2001
Posted By: Alvan Hengge, Faculty, Chemistry and Biochemistry, Utah State University
Area of science: Biochemistry
ID: 985284041.Bc
Message:

Catalases normally utilize a ferric ion (Fe (III)) as part of their 
catalytic machinery. The ferric ion is at the center of a heme group.  You 
have probably heard of hemes before – hemoglobin is the compound that makes 
your blood red.  You can see a nice picture of a heme, with its bound iron, 
at: http://www.madsci.org/posts/archives/dec96/847573455.Bc.r.html

Other metal ions can substitute for the ferric ion in the heme, and carry 
out the role usually performed by the ferric ion in catalysis, but as you 
have observed, they are not as effective at catalyzing the reaction.   

When an enzyme is in a solution containing other metal ions, these ions can 
displace the ferric ion from the heme.  There will be an equilibrium between 
heme with bound ferric ion and that with the other competing ion; in other 
words, some of the enzyme molecules will have a heme with a ferric ion 
bound, others will have a copper ion in the heme.  In most solutions the 
concentration of the enzyme is very low compared to the concentration of 
other species (in your case, copper sulfate).  Enzyme concentrations are 
typically in the nanomolar range.  Thus when enzyme containing ferric ion is 
added to a solution containing a micromolar or millimolar concentration of 
copper ions (which would be 1,000 and 1,000,000 times more concentrated than 
nanomolar), the equilibrium will lie far to the side of the copper bound 
form.   



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