The first glycolysis rate-limiting enzyme is under various allosteric regulations. This protein is nearly inactive because of inhibition by ( ) under physiological conditions. The activity is restored by ( ), its most potent allosteric activator.

a. AMP :::: citrate
b. AMP :::: Fru-2,6-P2
c. ATP :::: citrate
d. ATP :::: Fru-2,6-P2
e. All of these

Phosphofructokinase-1 is the enzyme that catalyzes the formation of fructose-1,6-bisphosphate from fructose-6-phosphate and ATP. The phosphofructokinase step is the first rate-limiting step of glycolysis.

Phosphofructokinase-1 activity is allosterically regulated. Its activity is increased whenever the cell's ATP supply is depleted or when its breakdown products, ADP and AMP accuulates in he cell. However, it is inhibited when the cell is amply supplied with ATP.

The activity of phosphofructokinase-1 is restored by fructose-2,6-bisphosphate, its most potent activator.

From the given options:

a. AMP :::: citrate is wrong because AMP increases the activity of phosphofructokinase-1 and citrate is not its activator but an inhibitor

b. AMP :::: Fru-2,6-P2 is wrong because AMP increases its activity same as fructose-2,6-bisphosphate

c. ATP :::: citrate is wrong because both citrate and ATP are inhibitors

d. ATP :::: Fru-2,6-P2 is correct as explained above

e. All of these is wrong because of the other wrong options above.