Phosphofructokinase-1 (PFK-1) is activated by AMP, ADP, fructose-2,6-bisphosphate, and inhibited by ATP, citrate, and H+. During intense exercise, glycolysis accelerates paradoxically despite a transient fall in pH. Which mechanism overrides the H+-mediated inhibition of PFK-1?

• A Glucagon-stimulated fructose-2,6-bisphosphate synthesis activates PFK-1
• B Sharp rise in AMP due to adenylate kinase reaction (2 ADP → ATP + AMP) powerfully activates PFK-1 ✓
• C Citrate levels fall during exercise, relieving inhibition of PFK-1
• D Insulin secretion during exercise phosphorylates and activates PFK-1 directly

Explanation

During intense exercise, ATP is consumed rapidly and ADP accumulates. The adenylate kinase reaction (2 ADP → ATP + AMP) generates AMP in large amounts. AMP is the most potent allosteric activator of PFK-1, raising its activity enough to overcome the inhibitory effect of the mild pH fall. Glucagon is not secreted during exercise, and insulin does not directly phosphorylate PFK-1. Citrate does fall, but its contribution is secondary to the AMP surge.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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