The enzyme phosphofructokinase catalyzes the reaction: fructose-6-phosphate + ATP fructose-1,6-bisphosphate + ADP The diagram below shows the sites of interaction of ATP with the enzyme. The enzyme kinetics is depicted in the graph below. ATP at active site Fructose- 1,6-bisphosphate at active site Quote Low ATP ATP at regulatory site Reaction rate High ATP Concentration of fructose-6-phosphate How is it possible for ATP to act as a substrate for the enzyme and at the same time cause an inhibition in enzyme activity at high concentration?