What is the effect of negative allosteric ligands on Km?

Negative allosteric ligands bind to an enzyme at a site distinct from the active site, leading to a conformational change in the enzyme structure. This change typically reduces the enzyme's affinity for its substrate.

Km, or the Michaelis constant, is a measure of how effectively a substrate binds to an enzyme; a higher Km indicates lower affinity. When a negative allosteric ligand is present, the binding of the substrate becomes less favorable due to the altered enzyme conformation. As a result, a higher concentration of substrate is required to achieve half of the maximum reaction rate, which translates to an increase in Km.

Thus, the presence of negative allosteric ligands increases Km by decreasing the enzyme's affinity for the substrate, leading to the correct conclusion that their effect is to elevate the Km value.