Control of glycolytic flux: Phosphofructokinase-1 (PFK-1) is allosterically inhibited and activated, respectively, by which pair of effectors under typical cellular conditions?

Introduction / Context:
PFK-1 commits fructose-6-phosphate to glycolysis and is a central control node. Understanding its allosteric regulation explains how cells tune energy production to demand.

Given Data / Assumptions:

• ATP acts both as a substrate and a feedback inhibitor of PFK-1.
• ADP/AMP and fructose-2,6-bisphosphate are well-known activators that relieve ATP inhibition.
• Citrate signals abundant biosynthetic precursors and inhibits PFK-1 in many tissues.

Concept / Approach:
At high energy charge, ATP binds an allosteric site, decreasing PFK-1 affinity for fructose-6-phosphate. When ADP (and AMP) accumulate, they activate PFK-1, promoting glycolytic flux. Among the provided pairs, “ATP and ADP” best matches the classic inhibited/activated pairing.

Step-by-Step Solution:
List inhibitors: ATP (feedback), citrate (tissue dependent). List activators: ADP, AMP, and fructose-2,6-bisphosphate. From options, choose the pair that correctly states an inhibitor first and an activator second. Thus, select “ATP and ADP.”

Verification / Alternative check:
Biochemical assays show ATP shifts the PFK-1 activity curve to require higher fructose-6-phosphate; ADP/AMP reverse this effect.

Why Other Options Are Wrong:
PEP mainly regulates pyruvate kinase; AMP and Pi (b) are both activators, not an inhibit/activate pair; citrate and ATP (d) are both inhibitory; fructose-2,6-bisphosphate is an activator, not paired with a specific inhibitor in option (e).

Common Pitfalls:
Forgetting that ATP can inhibit a step it fuels; mixing regulators of different enzymes.

Final Answer:
ATP and ADP.