Phosphofructokinase Catalyzes the Phosphorylation of Fructose -Phosphate to Form Fructose

Multiple Choice

Phosphofructokinase catalyzes the phosphorylation of fructose -phosphate to form fructose ,-bisphosphate. ATP is the phosphate donor and also inhibits phosphofructokinase. How can ATP act as a substrate and as a feedback inhibitor?

A) The formation of fructose 1,6-bisphosphate is forced toward completion because standard free energy for the reaction is negative.
B) There are two ATP-binding sites on the enzyme; a catalytic site with low affinity and a regulatory binding site with high affinity. At high ATP levels, the enzyme is inhibited fully.
C) There are two ATP-binding sites on the enzyme; a catalytic site with a high affinity for ATP, and a regulatory site with low ATP affinity. The enzyme is shut down only at high ATP concentrations when the energy charge is high.
D) There is a single ATP-binding site; binding ATP lowers the probability of reaction for a short time, even after ATP is unbound. Thus a high ATP concentration inhibits the reaction.
E) none of the above