ATP Is a Cosubstrate of the Enzyme PFK-1

question 9

Multiple Choice

ATP is a cosubstrate of the enzyme PFK-1.In most species ATP is also an inhibitor of PFK-1 at higher concentrations.This seems to violate Le Chatelier's Principle.Which statement below would provide a suitable explanation?

• A)PFK-1 must be phosphorylated by ATP in the active site and the phosphorylated PFK-1 must be the less active form.
• B)There must be another cofactor interacting with ATP at high concentrations to achieve inhibition of PFK-1.
• C)ATP actually activates the reverse of the reaction preceding the PFK-1 step in the pathway.It likely has no direct effect on PFK-1.
• D)There are two sites on PFK-1 that bind ATP.One is the active site;the other is the regulatory site where inhibition occurs.

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