Which of the following glycolytic enzyme is used in gluconeogenesis ?
**Core Concept**
Gluconeogenesis is a metabolic pathway that generates glucose from non-carbohydrate sources, such as lactate, glycerol, and certain amino acids. This process is crucial for maintaining blood glucose levels during fasting or starvation. The gluconeogenic pathway involves a series of enzyme-catalyzed reactions that convert these non-carbohydrate sources into glucose.
**Why the Correct Answer is Right**
One of the key enzymes involved in gluconeogenesis is **Phosphoenolpyruvate Carboxykinase (PEPCK)**. PEPCK catalyzes the conversion of oxaloacetate to phosphoenolpyruvate (PEP), a crucial step in the gluconeogenic pathway. This enzyme is unique in that it is also involved in glycolysis, where it catalyzes the conversion of PEP to pyruvate. However, when glucose is abundant, the enzyme is inhibited, and when glucose is low, it is activated, allowing for the efficient conversion of non-carbohydrate sources into glucose.
**Why Each Wrong Option is Incorrect**
* **Option A:** **Hexokinase** is a key enzyme in glycolysis that catalyzes the conversion of glucose to glucose-6-phosphate. While it is essential for glycolysis, it is not directly involved in gluconeogenesis.
* **Option B:** **Pyruvate Kinase** is another glycolytic enzyme that catalyzes the conversion of phosphoenolpyruvate (PEP) to pyruvate. Like hexokinase, it is not directly involved in gluconeogenesis.
* **Option D:** **Fructose-1,6-Bisphosphatase** is an enzyme involved in gluconeogenesis, but it is not the correct answer because it catalyzes a different step in the pathway.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that gluconeogenesis is a vital mechanism for maintaining blood glucose levels during fasting or starvation. However, excessive gluconeogenesis can lead to hyperglycemia, particularly in patients with type 2 diabetes or those taking glucocorticoids.
**Correct Answer: C. Phosphoenolpyruvate Carboxykinase**