In the context of enzyme kinetics, which type of inhibition does not affect the binding affinity of the substrate to the active site?

In non-competitive inhibition, the inhibitor binds to an allosteric site on the enzyme rather than the active site where the substrate binds. This type of inhibition does not affect the binding affinity of the substrate to the active site because the substrate can still bind to the enzyme regardless of whether the inhibitor is present. However, when the non-competitive inhibitor binds to the enzyme, it alters the enzyme's conformation, reducing its activity and preventing the conversion of substrate to product.

Since the substrate can still bind effectively and form an enzyme-substrate complex in the presence of a non-competitive inhibitor, the apparent affinity of the enzyme for the substrate remains unchanged. This distinguishes non-competitive inhibition from competitive inhibition, where the inhibitor competes directly with the substrate for the active site, reducing the binding of the substrate and effectively increasing the apparent Km (Michaelis constant).

In contrast, uncompetitive inhibition requires that the substrate is bound to the enzyme before the inhibitor can bind, which modifies both the binding and catalytic properties of the enzyme. Irreversible inhibition involves the formation of a covalent bond between the inhibitor and the enzyme, permanently inactivating the enzyme, which also significantly alters its activity in relation to substrate binding. Thus, non-competitive inhibition