A series of enzymes catalyze the reactions in the metabolic pathway X → Y → Z → A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme. With respect to the enzyme that converts X to Y, substance A functions as ________.
A) an allosteric inhibitor
B) the substrate
C) an intermediate
D) a competitive inhibitor

Question

Quizplus · Accepted Answer

Substance A binds to the enzyme that converts X to Y at a position remote from its active site and decreases its activity. This is a characteristic feature of an allosteric inhibitor which binds to the regulatory site of the enzyme instead of the active site, causing a conformational change that reduces the enzyme's catalytic activity. Option B is incorrect because the substrate is the molecule that undergoes a chemical transformation, in this case, X to Y. Option C is incorrect because an intermediate is a molecule that is formed in a reaction and subsequently utilized in a later reaction in the pathway. Option D is incorrect because competitive inhibitors bind to the active site of the enzyme, leading to reduced substrate binding and catalytic activity. However, substance A does not bind to the active site of the enzyme.

A Series of Enzymes Catalyze the Reactions in the Metabolic