The regulation of phosphofructokinase-1 (PFK-1) is critical for glycolytic flux. Which combination of effectors represents a physiological 'fed state' activation profile of PFK-1?

• A High ATP, high citrate — activating PFK-1
• B High ATP, low AMP, high H+ — inhibiting PFK-1
• C Low fructose-2,6-bisphosphate, high citrate — activating PFK-1
• D High AMP, high fructose-2,6-bisphosphate — activating PFK-1 ✓

Explanation

PFK-1 is the key regulated enzyme of glycolysis. In the fed state: (1) high AMP (relative to ATP) activates PFK-1 allosterically; (2) fructose-2,6-bisphosphate (F2,6-BP, produced by PFK-2 which is active when insulin is high/glucagon is low) is the most potent allosteric activator of PFK-1, overcoming ATP inhibition. F2,6-BP is synthesized from F6P by the bifunctional enzyme PFK-2/FBPase-2; insulin activates the kinase domain (PFK-2) while glucagon activates the phosphatase domain (FBPase-2). High ATP and citrate are inhibitory signals indicating energy sufficiency.

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

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