Local conditions such as a change in temperature and pH affect the activity of an enzyme.

Local conditions can affect an enzyme’s active site and, therefore, the rate at which a chemical reaction can proceed. Increasing the environmental temperature generally increases reaction rates because the molecules are moving more quickly and are more likely to come into contact with each other.

However, increasing or decreasing the temperature outside of an optimal range can affect chemical bonds within the enzyme and change its shape. If the enzyme changes shape, the active site may no longer bind to the appropriate substrate and the rate of reaction will decrease. Dramatic changes to the temperature and pH will eventually cause enzymes to denature.

Key Points

• When the temperature is reduced, the activity of an enzyme is affected.

• When the temperature is increased, the activity of an enzyme is increased. However, an excessive rise in temperature can cause denaturation of the enzyme.

• Increased or decreased pH from the optimal pH reduces enzyme activity.

Key Terms

denature: To destroy the characteristic properties of (a protein or other biological macromolecule) by heat, acidity, or other effects that disrupt its molecular conformation.

optimal: The best or most favorable conditions.

active site: The active site is the part of an enzyme to which substrates bind and where a reaction is catalyzed.