Hexokinase, that catalyzes the first irreversible step of glycolysis, is inhibited by glucose 6-phosphate.   Thus  when  PFK  is  inhibited and  fructose  6-phosphate builds  up and so does glucose  6-phosphate  due to these two metabolites  are in equilibrium  by phosphoglucoisomerase. Hexokinase inhibition then reinforces the inhibition at the PFK step. At first sight this seems commonly as it is usually the first irreversible step of a pathway (the committed step) that is the major control step. On this basis, it may appear in which hexokinase should be the main control enzyme not PFK.  Furthermore,   glucose 6-phosphate the product of the hexokinase reaction can also feed into glycogen synthesis or the pentose phosphate pathway. Thus the first irreversible step which is exclusive to glycolysis is which catalyzed by PFK and therefore this is the main control step.