Which of the following is an allosteric regulator of the enzyme phosphofructokinase in glycolysis?
Correct: A
Phosphofructokinase is a key regulatory enzyme. ATP and NADH act as negative allosteric inhibitors when energy is sufficient. AMP signals low energy and activates it. Fructose 2,6-bisphosphate acts as a positive modulator. The question focuses on ATP, which directly inhibits the enzyme in high-energy states, making A the correct answer.