What type of inhibitor binds at a different active site and cannot be overcome by increasing substrate concentration?

The correct answer is that noncompetitive inhibitors bind to a different active site on the enzyme, which is distinct from the active site where the substrate binds. This unique mechanism means that the inhibitor can attach to the enzyme whether or not the substrate is present.

Since noncompetitive inhibitors affect the enzyme's function regardless of substrate concentration, increasing the concentration of substrate will not reverse their inhibitory effect. This is in contrast to competitive inhibitors, which directly compete with the substrate for the active site, and their effects can be alleviated by increasing substrate levels. Uncompetitive inhibitors also bind differently but only attach to the enzyme-substrate complex, thereby requiring the substrate to be present for their action. Feedback inhibitors are typically involved in metabolic pathways, whereby the end product inhibits an earlier step, rather than fitting the definition provided in the question about binding at a different site.

Thus, noncompetitive inhibition specifically characterizes the binding interaction at a site not interfering with the substrate’s ability to bind, making it uniquely distinct in its mode of action.