Fructose-1-P compete with fructose-6-P for the binding site n a regulatory protein. So, in the presence of fructose-1-P, fructose-6-P looses its inhibitory effect.

Fructose-1-P is produced during fructose degradation. In this case, glucose is preferiantially stored as glycogen whereas fructose is degraded by the glycolytic pathway. So, this first step must occur to phosphorylate glucose for glycogen biosynthesis.