The glycolysis is regulated by
## **Core Concept**
Glycolysis is a metabolic pathway that converts glucose into pyruvate, releasing energy and forming ATP and NADH in the process. It is a crucial step in cellular respiration and energy production. The regulation of glycolysis is vital for maintaining energy homeostasis in cells.
## **Why the Correct Answer is Right**
The correct answer, **Phosphofructokinase (PFK)**, is a key regulatory enzyme in the glycolytic pathway. PFK catalyzes the conversion of fructose-6-phosphate into fructose-1,6-bisphosphate, which is a committed and irreversible step in glycolysis. This enzyme is a critical control point because it determines the rate at which glucose is funneled into the glycolytic pathway. PFK is allosterically inhibited by ATP and citrate, indicating a sufficient energy status in the cell, and is activated by AMP, signaling low energy levels.
## **Why Each Wrong Option is Incorrect**
- **Option A:** Hexokinase is an enzyme involved in the first step of glycolysis, converting glucose into glucose-6-phosphate. While it is important for initiating glycolysis, especially in certain tissues, it is not the primary regulatory step for the entire glycolytic pathway.
- **Option B:** Pyruvate kinase catalyzes the final step of glycolysis, converting phosphoenolpyruvate (PEP) into pyruvate, generating one molecule of ATP per converted molecule. It is indeed a regulatory enzyme but is not considered the primary regulatory step compared to phosphofructokinase.
- **Option D:** Glucose-6-phosphate isomerase is an enzyme in the glycolytic pathway that converts glucose-6-phosphate into fructose-6-phosphate. While essential for glycolysis, it is not a key regulatory step.
## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **phosphofructokinase-1 (PFK-1) deficiency** leads to Tarui disease, a rare genetic disorder characterized by glycogen storage disease type VII. This condition highlights the importance of PFK in glycolytic regulation and energy metabolism.
## **Correct Answer:** C. Phosphofructokinase.