Question

A noncompetitive inhibitor will affect the ________ of an enzymatic reaction.

1) Km
2) Vmax
3) S
4) P
5) both choices A and B

Answer 1

A noncompetitive inhibitor affects the maximal velocity (Vmax) of an enzymatic reaction because it binds to the enzyme at an allosteric site and alters its conformation, which lowers the rate at which the enzyme converts substrate to product without changing the substrate's affinity for the enzyme (Km). The correct option is 2). Vmax

Step-by-step explanation:

A noncompetitive inhibitor will affect the Vmax (maximum velocity) of an enzymatic reaction, but it does not alter the Km (Michaelis constant) value. This is because a noncompetitive inhibitor can bind to both the enzyme without the substrate and the enzyme-substrate complex, at a site that is distinct from the active site.

This binding changes the enzyme's conformation in a way that prevents the effective catalysis of the substrate into product, thereby reducing the maximal reaction rate (Vmax). However, since the inhibitor does not compete directly with the substrate for the active site, the apparent affinity of the enzyme for the substrate (Km) remains constant. Therefore, the correct option is 2) Vmax.