## **Core Concept**
Fluoride is known to inhibit glycolysis, particularly in the context of preserving blood glucose levels during laboratory testing. The key enzymes involved in glycolysis are targeted by fluoride.

## **Why the Correct Answer is Right**
The correct answer targets the enzyme **Enolase**. Enolase is a glycolytic enzyme that catalyzes the conversion of 2-phosphoglycerate (2-PGA) to enolpyruvate (ENO), which then goes on to become phosphoenolpyruvate (PEP). Fluoride ions (F-) inhibit enolase by forming a complex with phosphate and magnesium ions, effectively blocking this step in glycolysis.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Hexokinase is the first committed step of glycolysis, converting glucose into glucose-6-phosphate. It is not directly inhibited by fluoride.
- **Option B:** Phosphofructokinase-1 (PFK-1) is another key regulatory enzyme in glycolysis, converting fructose-6-phosphate into fructose-1,6-bisphosphate. While it is a crucial step, it is not directly inhibited by fluoride.
- **Option D:** Pyruvate kinase is involved in the final step of glycolysis, converting phosphoenolpyruvate (PEP) into pyruvate. This enzyme is not directly inhibited by fluoride.

## **Clinical Pearl / High-Yield Fact**
A high-yield fact to remember is that fluoride is used in tubes for blood glucose testing because it inhibits glycolysis in vitro, thereby preserving the glucose level and providing an accurate measurement. This is particularly important in clinical settings where blood glucose levels need to be accurately determined.

## **Correct Answer:** . Enolase