What effect does non-competitive inhibition have on enzyme activity?

Non-competitive inhibition occurs when an inhibitor binds to an enzyme in a manner that is independent of the substrate binding. This type of inhibition affects the enzyme's activity by reducing the overall amount of available active enzyme, effectively lowering the maximum reaction rate (Vmax). Although the substrate can still bind to the enzyme, the presence of the inhibitor renders some of the enzyme inactive, thus decreasing the maximum rate at which the enzyme can catalyze the reaction.

In terms of enzyme kinetics, non-competitive inhibitors do not affect the affinity of the enzyme for the substrate, which means the Michaelis constant (Km) remains unchanged. This distinguishes non-competitive inhibition from other forms of inhibition, such as competitive inhibition, where the maximum reaction rate remains the same, but the Km increases, indicating a reduced affinity for the substrate.

Therefore, non-competitive inhibition directly decreases the maximum reaction rate, making it the correct response to this question.