When yeast or muscle is exposed to oxygen, the rate of glucose consumption falls sharply compared with anaerobic conditions. What best explains this observation?
- A Oxygen directly inhibits hexokinase, reducing glucose phosphorylation
- B Oxygen activates pyruvate dehydrogenase kinase, shutting down glucose oxidation entirely
- C Oxidative phosphorylation raises ATP and citrate levels, and both allosterically inhibit phosphofructokinase-1 ✓
- D Oxygen induces fructose-2,6-bisphosphatase, lowering fructose-2,6-bisphosphate in all tissues equally
Correct answer: C. Oxidative phosphorylation raises ATP and citrate levels, and both allosterically inhibit phosphofructokinase-1
Explanation
The Pasteur effect reflects feedback control at phosphofructokinase-1, the rate-limiting enzyme of glycolysis. When oxygen permits oxidative phosphorylation, cellular ATP rises and citrate accumulates as TCA cycle flux increases; both are negative allosteric effectors of PFK-1, slowing glucose use. Oxygen does not directly inhibit hexokinase, pyruvate dehydrogenase kinase is inhibited (not activated) by pyruvate, and fructose-2,6-bisphosphate changes are hormone driven and tissue specific, not a uniform response to oxygen.
Reference: Lehninger Principles of Biochemistry, 8th ed.
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