Question

pyruvate kinase, a key enzyme in the glycolysis pathway, is inhibited by the amino - acid alanine. the ability of alanine to inhibit this enzyme is affected by increasing the concentration of substrate.

which of the following best explains the mechanism by which alanine inhibits pyruvate kinase activity?
a alanine binds to an allosteric site of the enzyme, changing the shape of the enzymes active site.
b alanine increases the enzyme - substrate binding and the enzyme becomes saturated.
c alanine is a competitive inhibitor that reversibly binds to the active site of the enzyme.
d alanine binds to the substrate, preventing the substrate from being able to bind to the active site of the enzyme.

Explanation:

Alanine is an allosteric inhibitor of pyruvate kinase. Allosteric inhibitors bind to an allosteric site of the enzyme, causing a conformational change in the active - site, which reduces enzyme activity. Option A correctly describes this mechanism. Option B is incorrect as alanine is an inhibitor, not something that increases enzyme - substrate binding. Option C is wrong because alanine is an allosteric, not a competitive inhibitor. Option D is incorrect as alanine binds to the enzyme, not the substrate.

Answer:

A. Alanine binds to an allosteric site of the enzyme, changing the shape of the enzyme's active site.