Subject: Why might the reaction rate of enzyme catalysis be the same at a pH of 7&10

I was testing a 100% catalase solution and pH buffered hydrogen peroxide 
solutions at the pHs of 4, 7, and 10.  I was trying to find the reaction rate 
of enzyme catalysis, and my reaction rates for the pHs of 7 and 10 were 2.81 
mm/second.  I got the reaction rate of 1.5mm/second.  I was wondering if you 
could tell me why i got these results.  This experiment was WARDS Enzyme 
Catalysis, and i was measuring the reaction rate by dipping a filter paper 
disc into the catalase solution for 5 seconds, then blotting it dry for 5 
seconds, then dropping it into one of the hydrogen peroxides and timing from 
the time it enters the hydrogen peroxide, letting it sink to the bottom, and 
then when it comes up to the surface of the hydrogen peroxide, stopping the 
timing.  I would measure the depth that the paper had traveled.  I would 
divide the depth by the time to get the reaction rate.  (pH 4- 45mm/30 sec) 
(pHs 7 and 10- 45mm/16 sec)

Re: Why might the reaction rate of enzyme catalysis be the same at a pH of 7&10