Three factors that control enzyme activity are: pH, Temperature, Concentrations of enzyme and substrate

pH: the optimum (best) in most living things is close to 7 (neutral). High or low pH levels usually slow enzyme activity

Temperature: strongly influences enzyme activity
* optimum (best) temperature 35-40 C.
* reactions proceed slowly below optimal temperatures
* above 45 C. most enzymes are denatured (change in their shape so the enzyme active site no longer fits with the substrate and the enzyme can't function)

Concentrations of Enzyme and Substrate
When there is a fixed amount of enzyme and an excess of substrate molecules the rate of reaction will increase to a point and then level off.

-Leveling off occurs because all of the enzyme is used up and the excess substrate has nothing to combine with.

-If more enzyme is available than substrate, a similar reaction rate increase and leveling off will occur. The excess enzyme will eventually run out of substrate molecules to react with.