## **Core Concept**
Fluoride is known to inhibit a key enzyme in the glycolytic pathway. This pathway is crucial for glucose metabolism in cells, producing energy in the form of ATP. The inhibition of this pathway can affect cellular energy production.

## **Why the Correct Answer is Right**
The correct answer, **Enolase**, is an enzyme in the glycolytic pathway that catalyzes the conversion of 2-phosphoglycerate (2-PGA) to enolpyruvate (ENO), which then goes on to become phosphoenolpyruvate (PEP). Fluoride ions (F-) inhibit this enzyme, **Enolase**, by forming a complex with phosphate and the substrate, thereby blocking the conversion. This inhibition is significant in the context of glycolysis and cellular metabolism.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Hexokinase is an enzyme that phosphorylates hexoses (six-carbon sugars) to form hexose phosphate. It is not directly inhibited by fluoride.
- **Option B:** Phosphofructokinase is another enzyme in the glycolytic pathway, crucial for the conversion of fructose-6-phosphate into fructose-1,6-bisphosphate. While it is a key regulatory enzyme, it is not inhibited by fluoride.
- **Option C:** Pyruvate kinase is involved in the final step of glycolysis, converting phosphoenolpyruvate (PEP) into pyruvate, generating one molecule of ATP per converted molecule. It is not directly inhibited by fluoride.

## **Clinical Pearl / High-Yield Fact**
A high-yield fact to remember is that fluoride inhibition of enolase in the glycolytic pathway is the basis for using fluoride as an inhibitor of glycolysis in blood samples collected for glucose measurement, thereby preventing in vitro glycolysis and ensuring accurate glucose levels.

## **Correct Answer:** D. Enolase