## **Core Concept**
Sodium fluoride (NaF) is known to inhibit glycolysis, a metabolic pathway that converts glucose into pyruvate, releasing energy. This inhibition occurs at a specific step in the glycolytic pathway.

## **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). Sodium fluoride (NaF) acts as an inhibitor of this enzyme. It forms a complex with phosphate and magnesium ions, which are essential for the enolase enzyme's activity, thereby inhibiting the enzyme and effectively blocking glycolysis.

## **Why Each Wrong Option is Incorrect**
- **Option A: Hexokinase** - Hexokinase is the enzyme responsible for the first step of glycolysis, converting glucose into glucose-6-phosphate. It is not inhibited by sodium fluoride.
- **Option B: Phosphofructokinase-1 (PFK-1)** - PFK-1 is another key regulatory enzyme in the glycolytic pathway, converting fructose-6-phosphate into fructose-1,6-bisphosphate. While it is a crucial regulatory step, it is not directly inhibited by sodium fluoride.
- **Option D: Pyruvate Kinase** - Pyruvate kinase is the enzyme that catalyzes the final step of glycolysis, converting phosphoenolpyruvate (PEP) into pyruvate. Though it is essential for glycolysis, its activity is not directly affected by sodium fluoride.

## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that fluoride inhibits glycolysis, which has implications for blood glucose testing. When blood samples are collected in tubes containing fluoride (often used for alcohol testing), glycolysis in the sample is inhibited, helping to preserve the glucose level for accurate measurement.

## **Correct Answer:** . Enolase