Question

What does the KI' for a noncompetitive inhibitor mean?

a) Inhibitor dissociation constant
b) Substrate concentration at half-maximal velocity
c) Inhibitor concentration at half-maximal velocity
d) Competitive inhibition constant

Answer 1

The Ki' for a noncompetitive inhibitor is the inhibitor dissociation constant, indicating the concentration needed for half-maximal inhibition of the enzyme, and the correct answer is option (a).

Step-by-step explanation:

The Ki' for a noncompetitive inhibitor represents the inhibitor dissociation constant, which is a measure of the affinity of the inhibitor for the enzyme. It specifies the concentration of inhibitor needed to reach half-maximal inhibition of the enzyme activity. This is different from the Michaelis-Menten constant (Km), which measures the substrate concentration at half-maximal velocity of the enzyme-catalyzed reaction. In the presence of a noncompetitive inhibitor, binding occurs at an allosteric site, which does not compete with the substrate binding site, and causes a conformational change that diminishes the enzyme’s activity, with excess substrate unable to reverse the inhibitory effect. As a result, the answer to the student's question is option (a) Inhibitor dissociation constant.