Effect of Temperature on an Enzyme-Catalyzed Reaction

Velocity increase with temperature: The reaction velocity increases with temperature until a peak velocity is reached (Fig. 1). This increase is the result of the increased number of substrate molecules having sufficient energy to pass over the energy barrier and form the products of the reaction.

Figure 1 Effect of temperature on an enzyme-catalyzed reaction.

 Velocity decrease with higher temperature: Further elevation of the temperature causes a decrease in reaction velocity as a result of temperature-induced denaturation of the enzyme (see Fig. 1).
The optimum temperature for most human enzymes is between 35°C and 40°C. Human enzymes start to denature  at temperatures above 40°C, but thermophilic bacteria found in hot springs have optimum temperatures of 70°C.