What is the effect of a competitive inhibitor on Km and Vmax?

A competitive inhibitor affects the enzyme kinetics by influencing the Michaelis-Menten parameters, specifically Km and Vmax. In the presence of a competitive inhibitor, there is a competition between the substrate and the inhibitor for the active site of the enzyme.

When a competitive inhibitor is present, more substrate is required to reach half the maximum reaction velocity, which effectively increases the Km (the Michaelis constant). This increase indicates a decreased affinity of the enzyme for the substrate because the inhibitor is occupying the active site and makes it harder for the substrate to bind.

Importantly, Vmax remains unchanged in the presence of a competitive inhibitor. This is because if the concentration of the substrate is significantly increased, it can outcompete the inhibitor for the enzyme's active site and achieve the maximum velocity. Therefore, while Km increases due to the reduced affinity under these conditions, Vmax of the reaction does not change, reflecting that the enzyme can still operate at its maximum capacity when substrate concentration is sufficiently high.