What happens to Vmax during competitive inhibition?

In the context of enzyme kinetics, competitive inhibition is characterized by the inhibitor competing with the substrate for the active site of the enzyme. When a competitive inhibitor is present, it can bind to the active site, preventing the substrate from accessing it. However, this type of inhibition does not affect the overall number of active enzyme molecules available; it only reduces the likelihood of substrate binding when the inhibitor is present.

As the concentration of substrate increases, the effect of the competitive inhibitor can be overcome, which means that at sufficiently high substrate concentrations, the enzyme can achieve its maximum rate of reaction (Vmax) as if no inhibitor were present. Therefore, while the apparent affinity of the enzyme for the substrate (often quantified by the Michaelis-Menten constant, Km) increases in the presence of a competitive inhibitor, the Vmax itself remains unchanged because the enzyme can ultimately bind substrate in excess amounts.

This fundamental characteristic distinguishes competitive inhibition from other forms of inhibition, such as non-competitive or uncompetitive inhibition, which do affect Vmax. Thus, during competitive inhibition, Vmax stays the same, reflecting the capacity of the enzyme to catalyze a reaction when all active sites are occupied by the substrate.