Final answer:
Noncompetitive inhibition affects the maximum reaction rate (Vmax) of an enzyme by binding to an allosteric site but does not change the Michaelis constant (Km), which reflects the substrate's binding affinity to the enzyme.
Step-by-step explanation:
The effect of noncompetitive inhibition on the Michaelis constant (Km) is distinct compared to other types of inhibition. Noncompetitive inhibitors bind to an allosteric site on the enzyme, which is different from the active site where substrates bind. This binding results in a conformational change in the enzyme that either prevents the enzyme-substrate complex from forming at its normal rate or inhibits the production of products from the enzyme-substrate complex once it is formed.
Because the inhibitor does not compete with the substrate for the enzyme's active site, increased substrate concentration does not overcome noncompetitive inhibition. As a result, noncompetitive inhibitors decrease the enzyme's maximum reaction rate (Vmax), but they do not change the Michaelis constant (Km), which reflects the binding affinity between enzyme and substrate. A high Km value indicates weak enzyme-substrate binding, whereas a low Km indicates strong binding. In the presence of a noncompetitive inhibitor, the enzyme activity cannot reach the normal maximum rate, even as substrate concentration increases, leading to a lower Vmax.
In summary, noncompetitive inhibition affects Vmax while leaving Km unchanged. This is because the substrate can still bind to the enzyme with the same affinity as without the inhibitor present, but the overall reaction rate is reduced.