Glycolytic enzymes inhibited by fluoride
## **Core Concept**
The question tests knowledge of glycolytic pathway regulation, specifically focusing on the inhibitory effects of fluoride on glycolytic enzymes. Fluoride is known to inhibit glycolysis, and this property is utilized in certain laboratory tests. The key enzyme in this context is enolase.
## **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. The mechanism involves the formation of a complex between fluoride, phosphate, and the enzyme, effectively blocking the conversion and thereby inhibiting glycolysis. This is particularly relevant in clinical settings where fluoride is used as a glycolysis inhibitor in blood samples to preserve glucose levels for accurate measurement.
## **Why Each Wrong Option is Incorrect**
- **Option A: Hexokinase** - Hexokinase is the first enzyme in the glycolytic pathway, responsible for converting glucose into glucose-6-phosphate. It is not directly inhibited by fluoride.
- **Option B: Phosphofructokinase-1 (PFK-1)** - PFK-1 is a key regulatory enzyme in the glycolytic pathway, converting fructose-6-phosphate into fructose-1,6-bisphosphate. While it is a crucial point of regulation in glycolysis, it is not inhibited by fluoride.
- **Option D: Pyruvate Kinase** - Pyruvate kinase is another regulatory enzyme in glycolysis, catalyzing the final step where phosphoenolpyruvate is converted into pyruvate. It is not directly inhibited by fluoride.
## **Clinical Pearl / High-Yield Fact**
A key clinical application of fluoride's inhibitory effect on glycolysis is in the collection of blood samples for glucose measurement. Fluoride inhibits glycolysis in vitro, thereby preventing the consumption of glucose by cells in the blood sample and providing a more accurate measurement of blood glucose levels at the time of collection.
## **Correct Answer: C. Enolase**