Which type of inhibition does not change the Km but decreases Vmax?

The correct answer, noncompetitive inhibition, is characterized by its unique effect on enzyme kinetics. In this type of inhibition, the inhibitor can bind to the enzyme regardless of whether the substrate is present. As a result, noncompetitive inhibitors decrease the overall number of available active sites for the enzyme, leading to a decrease in the maximum reaction velocity (Vmax). However, since the substrate can still bind to the enzyme as usual, the apparent affinity of the enzyme for the substrate, represented by the Michaelis constant (Km), remains unchanged.

In competitive inhibition, the inhibitor competes with the substrate for the active site, which effectively raises the Km because a higher concentration of substrate is needed to achieve half-maximal enzyme activity. Irreversible inhibition leads to a permanent reduction in enzyme activity, which also affects Vmax but can sometimes alter Km depending on the specifics of the inhibition mechanism. Uncompetitive inhibition decreases both Km and Vmax because the inhibitor binds to the enzyme-substrate complex, preventing the conversion of substrate to product and thereby affecting the maximum rate as well as the affinity for the substrate.

Thus, noncompetitive inhibition stands out because it allows for the Km to remain the same, indicating that the substrate can still bind to the enzyme without alteration, while