Question

Why is Phosphofructokinase-1 reaction considered the key regulatory step in Glycolysis and not Hexokinase reaction?

Answer 1

Both reactions are irreversible and are considered to be important in the regulation of glycolysis pathway. However, phosphofructokinase-1 reaction is the first irreversible reaction specific for glycolysis. Hexokinase reaction can take place in case of other metabolic pathways, pentose phosphate pathway for example, while phosphofructokinase-1 reaction is present only in glycolysis. Secondly, phosphofructokinase-1 is an allosteric enzyme, which has a great number of activators and inhibitors. Phosphoenolpyruvate is one of the substances produced during glycolysis and it affects the functioning of phosphofructokinase-1, not hexokinase. In the same way, AMP, ATP and citrate also regulate the activity of phosphofructokinase-1