Fluoride ions inhibit which enzyme in glycolysis?

• A. Hexokinase
• B. Enolase
• C. Phosphofructokinase
• D. Pyruvate kinase

Answer: (B)

Fluoride ions inhibit enolase, the enzyme that catalyzes the dehydration of 2-phosphoglycerate to phosphoenolpyruvate in glycolysis. Blocking this step stops glycolysis downstream, reducing ATP production from glycolysis. The fluoride effect comes from forming a Mg2+-fluoride complex in the enolase active site, which mimics the transition state and prevents catalysis. The other enzymes listed—hexokinase, phosphofructokinase, and pyruvate kinase—are not inhibited by fluoride in this way, so glycolysis proceeds up to the enolase step but cannot complete to pyruvate.