The Pasteur effect refers to the inhibition of glycolysis by oxygen. Which mechanism best explains this phenomenon?

• A Oxygen directly inhibits hexokinase activity in the mitochondrial intermembrane space
• B Oxygen activates pyruvate dehydrogenase, preventing pyruvate from being reduced to lactate
• C NADH produced in glycolysis is directly oxidized by molecular oxygen, bypassing lactate dehydrogenase
• D Oxidative phosphorylation increases ATP and citrate levels, which allosterically inhibit phosphofructokinase-1 ✓

Explanation

The Pasteur effect occurs because aerobic ATP production via oxidative phosphorylation raises cytoplasmic ATP and citrate, which allosterically inhibit PFK-1, slowing glycolysis. Oxygen does not directly inhibit glycolytic enzymes. While NADH is oxidized via shuttles, this is not the primary regulatory mechanism. PDH activation is a consequence, not the cause, of the Pasteur effect.

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

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