b-galactosidase assay quetion

Shad Turner swturner at unixg.ubc.ca
Fri Nov 22 15:39:58 EST 1996

I'm an undergrad doing some assaying on b-galactosidase (using 
o-nitrophenol-b-galactoside as the substrate) from e.coli and 
some funny things are turning up. The thing I don't understand most and 
can't seem to find any information on the literature is that when adding 
lactose to the assay as an alternate chemical (while still including ONPG 
in the asasy,) the rate of formation of coloured product of o-nitrophenol 
increases with an increase in the concentration of added lactose. I would 
have thought that adding lactose would competitively inhibit the 
hydrolysis of ONPG. Is there possibly allostery going on? HELP!! I guess 
I don't really know enough about the enzyme itself. Any help would be 
much appreciated.


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