Q.44 Which of the following statements is/are correct about an uncompetitive inhibitor
of an enzyme?
(A) It binds to the substrate binding site of the enzyme only
(B) It binds to the enzyme-substrate complex only
(C) It reduces the Vmax of the enzyme
(D) It binds to both free enzyme and enzyme-substrate complex
Uncompetitive inhibitors bind exclusively to the enzyme-substrate complex, distinguishing them from other inhibition types. For the given multiple-choice question, options (B) and (C) are correct.
Correct Options
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(B) It binds to the enzyme-substrate complex only: This defines uncompetitive inhibition, where the inhibitor attaches to the ES complex at an allosteric site, forming an inactive ESI complex that prevents product formation.
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(C) It reduces the Vmax of the enzyme: By trapping the enzyme in the unproductive ESI state, uncompetitive inhibition lowers maximum velocity (Vmax) while also decreasing apparent Km due to enhanced substrate affinity in the ES complex.
Incorrect Options
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(A) It binds to the substrate binding site of the enzyme only: False, as uncompetitive inhibitors do not bind the active site or compete with substrate; they target a distinct site on the ES complex only.
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(D) It binds to both free enzyme and enzyme-substrate complex: Incorrect, since binding occurs solely with the ES complex, not free enzyme—this differentiates it from noncompetitive or mixed inhibition.
Key Effects on Kinetics
Uncompetitive inhibition yields parallel lines on Lineweaver-Burk plots, with increased y-intercept (1/Vmax rises) and x-intercept shifting left (Km decreases). This pattern confirms ES-specific binding and Vmax reduction without active site competition. Such inhibitors prove valuable in biochemistry for regulating enzymes at high substrate levels.
