More info on the isoenzyme question

Robert DiSilvestro rdisilvexx at smtp.service.ohio-state.edu
Wed Sep 3 12:59:10 EST 1997

I had posted about use of the term isozyme.  Since I have gotten a few 
questions about how "subtle" the structural differences are between forms, let 
me just give some specifics.  I had hesitated on this to avoid possibly
"blowing my cover"  as a reviewer.  The enzymes are the superoxide 
dismutases (SODs).  Two of them have active sites which contain copper and 
zinc, the other has an active site with manganese.  The MWs are quite 
different for all 3, and antibodies to one generally don't react with the 
other two.  Cells contain one of the Cu-Zn enzymes (mostly in the cytosol), 
and the one Mn enzyme (in the mitochondria).  The other SOD is secreted to the 
outside of cells and is called extracellular SOD.  Thus, these are three 
structurally distinct enzymes which have a similar enzyme activity.

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