Final answer:
The rate of reaction decreases when pH values exceed an enzyme's optimum pH, due to alterations in the enzyme's structure that affect its ability to catalyze reactions.
Step-by-step explanation:
When pH values are higher than an enzyme's optimum pH, the rate of reaction generally decreases. Enzymes have a specific pH at which they operate most effectively, and deviations from this optimum pH result in a reduced efficiency of the enzyme. For instance, if an enzyme has an optimum pH of 4.5, its activity will decline when the pH increases beyond this point. This behavior is due to the changes in the protein structure of the enzyme that affect its ability to bind substrates and catalyze reactions. At very high or very low pH levels, enzymes can become denatured, meaning their structure is irreversibly altered, leading to a loss of function.
The effectiveness of an enzyme's activity, including the rate of reaction, is dependent on the proper alignment and structural integrity of its active site. pH levels can alter the charge and shape of the active site, affecting the enzyme's ability to interact with its substrate. Therefore, at a pH higher than the optimum, the enzyme's performance decreases, and the reaction rate slows down.