In the presence of a noncompetitive inhibitor, Km remains unchanged. Which of the following statements is true?

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Multiple Choice

In the presence of a noncompetitive inhibitor, Km remains unchanged. Which of the following statements is true?

Explanation:
Noncompetitive inhibition changes how fast the reaction can proceed without changing how tightly the substrate binds. The inhibitor binds to a site other than the active site, so it doesn’t block substrate binding itself. Because the binding step isn’t affected, the apparent affinity for the substrate (Km) stays the same. What changes is the maximum rate (Vmax), since fewer enzyme molecules are effectively available to carry out the reaction. So Km remains unchanged while Vmax decreases. (Note: in some mixed cases, Km can shift, but for pure noncompetitive inhibition it does not.)

Noncompetitive inhibition changes how fast the reaction can proceed without changing how tightly the substrate binds. The inhibitor binds to a site other than the active site, so it doesn’t block substrate binding itself. Because the binding step isn’t affected, the apparent affinity for the substrate (Km) stays the same. What changes is the maximum rate (Vmax), since fewer enzyme molecules are effectively available to carry out the reaction. So Km remains unchanged while Vmax decreases. (Note: in some mixed cases, Km can shift, but for pure noncompetitive inhibition it does not.)

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