What effect does non-competitive inhibition have on Km?

Non-competitive inhibition refers to a type of enzyme inhibition where the inhibitor binds to an enzyme regardless of whether the substrate is present. This binding affects the overall turnover number (Vmax) of the enzyme but does not alter the affinity of the enzyme for the substrate, which is represented by Km (Michaelis constant).

Km is defined as the substrate concentration at which the reaction velocity is half of Vmax. In the case of non-competitive inhibition, since the inhibitor does not prevent the substrate from binding to the enzyme, the affinity for the substrate remains unchanged. Therefore, the Km value remains the same, indicating that the substrate concentration required to reach half-maximal velocity is not affected by the presence of the non-competitive inhibitor.

Consequently, since non-competitive inhibition does not influence Km, the correct understanding is that it has no effect on Km. This characteristic distinguishes non-competitive inhibition from competitive inhibition, where the Km would indeed be increased due to the competition between the substrate and the inhibitor for the active site of the enzyme. Thus, the correct response for the effect of non-competitive inhibition on Km is that it remains unchanged.