Answer:
Different Enzymes are effected differently. Most Enzymes have an optimum pH and Temperature though if the fall above or below this the rate at which an enzyme induces or canalizes reaction may be lowered or stopped completely(I am not aware if it can have a reverse effect, I do not believe so).
For example: The enzyme Pepsin has an optimal range of pH 1.5-3 anything outside this and Pepsin (a digestive enzyme in the stomach) will not work at full capacity. Temperature also affects Pepsin; it works best at 98.6oF to 107.6oF. After Pepsin reaches boiling, it stops working completely.