During competitive inhibition, what effect does it have on Km?

In the context of competitive inhibition, the key understanding revolves around how the presence of an inhibitor affects the enzyme's affinity for its substrate, which is directly reflected in the value of Km (the Michaelis constant).

When a competitive inhibitor is present, it competes with the substrate for binding to the active site of the enzyme. This competition means that at any given substrate concentration, a higher concentration of substrate is needed to reach half of the maximum velocity (Vmax) of the reaction. Consequently, while the maximum velocity (Vmax) remains unchanged because the inhibitor can be overcome by sufficiently high substrate concentrations, the apparent affinity of the enzyme for the substrate decreases.

This decrease in affinity manifests as an increase in Km. Thus, in the presence of a competitive inhibitor, the Km value increases, indicating that a greater concentration of substrate is required to achieve half the maximum reaction rate. Therefore, the correct choice is that competitive inhibition increases Km. Understanding this relationship is crucial in enzyme kinetics and helps in grasping how various factors can influence enzyme activity.