As the temperature of enzymes increase, enzymes will reach their optimal temperature. This is where the enzyme reaction rate will be the highest, however, if the temperature rises too high enzymes will start to denature and will no longer function as intended.
Enzymes also have an optimal pH at which they work. If the pH becomes too low or high, enzymes will start to unflold and proteins will no longer function, howver, if the pH is increased to the optimal pH, enzymes will fold back and function as intended.