Product binding sites on proteins

[William P. Tschantz]

Hi

I am looking for examples of proteins which have two product binding 
sites (the same product) if such a protein exists.  For example a protein 
which has one binding site where the product is formed and then is 
transferred to a second site on the enzyme.  I know this sounds kind of 
weird but i am trying to make sense of the data i have.  The only way i 
can explain it is if there is a second site present on the enzyme.  I can 
think of no examples except for ribosomes, which is not quite what i am 
looking for. 

Any help is greatly appreciated.

Thanks 

Bill