Answer: An enzyme has an optimum pH range in which it exhibits maximum activity. At low temperatures, an increase in temperature increases the rate of an enzyme-catalyzed reaction. At higher temperatures, the protein is denatured, and the rate of the reaction dramatically decreases. For many proteins, denaturation occurs between 45°C and 55°C, most biochemical reactions are carried out at lower temperatures, because enzymes are not stable at these higher temperatures and will denature after a few minutes.