NEET PG Medical – 2020 – Question – 34

Correct Answer – A
Ans: A. Km remains same, Vmax decreases Noncompetitive inhibition occurs when the inhibitor and substrate bind at different sites on the enzyme. The noncompetitive inhibitor can bind either the free enzyme or the ES complex, thereby preventing the reaction from occurring.
Effect on Vmax: Noncompetitive inhibition cannot be overcome by increasing the concentration of the substrate. Thus, noncompetitive inhibitors decrease the apparent Vmax of the reaction.
Effect on Km: Noncompetitive inhibitors do not interfere with the binding of substrate to enzyme. Thus, the enzyme shows the same Km in the presence or absence of the non-competitive inhibitor.
Effect on Lineweaver-Burk plot: Noncompetitive inhibition is readily differentiated from competitive inhibition by plotting 1/vo versus 1/[S] and noting that the apparent Vmax decreases in the presence of a non-competitive inhibitor, whereas Km is unchanged.

Ref- Lippincott’s Illustrated reviews,5th edition, Inhibition of Enzyme
Activity, pg 61.