Question

Why does it make physiological sense for the presence of excess ADP to increase the activity of phosphofructokinase in the EMP glycolytic pathway?

Answer 1

Answer: EMP pathway is the first process in generation of energy by cellular respiration. EMP pathway is regulated at several levels

One of the most important regulatory steps in EMP is catalytic action of phosphofructokinase(PFK). PFK catalyses the third reaction of EMP i.e.conversion of fructose-6-phosphate to fructose-1,6-diphosphate. It is an irreversible reaction, in presence of high levels of ATP , the ATP molecule binds to the allosteric site of PFK and inhibits the reaction which stops the glycolytic pathway since cell gets the signal that energy is abundant and there is no need to generate ATP. ATP negatively regulates the PFK by feedback inhibition.

.When the ATP is utilised the stores of ADP are rapidly converted to ATP and AMP by the enzyme adenylate cyclase,which increases the level of AMP

ADP+ADP gives rise to ATP+AMP

The opposite action takes place in presence of high AMP/ATP ratio

The high amount of AMP signals the cell that the ATP levels are low and the cellular respiration should take place, so high AMP positively regulates the EMP pathway. High level of ADP indirectly indicates that the cell is in need of energy and the product of its dephosphorylation i.e. AMP acts as a positive regulator of EMP pathway.