Insulin acts on which enzyme during glycolysis?
**Core Concept**
Insulin plays a crucial role in regulating glucose metabolism by influencing various enzymes involved in glycolysis. This process is essential for maintaining blood glucose levels within a normal range. Insulin's action on these enzymes helps to facilitate the uptake of glucose by cells, thereby reducing blood glucose levels.
**Why the Correct Answer is Right**
Insulin primarily acts on the enzyme phosphofructokinase-1 (PFK-1), which is a key regulatory step in glycolysis. By activating PFK-1, insulin enhances the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate, thereby promoting the flow of glucose through the glycolytic pathway. This action is mediated through the insulin signaling pathway, which involves the activation of protein kinase B (Akt) and subsequent phosphorylation of PFK-1.
**Why Each Wrong Option is Incorrect**
* **Option A:** Hexokinase is indeed an enzyme involved in glycolysis, but it is not the primary target of insulin action. Insulin does not directly influence hexokinase activity.
* **Option B:** Pyruvate kinase is another enzyme in glycolysis, but it is not the primary target of insulin action. Insulin's primary role is to enhance glucose uptake and utilization, not to promote the conversion of pyruvate to lactate.
* **Option D:** Glucose-6-phosphate dehydrogenase is an enzyme involved in the pentose phosphate pathway, not glycolysis. Insulin does not act on this enzyme.
**Clinical Pearl / High-Yield Fact**
Insulin's action on PFK-1 is a critical regulatory step in glycolysis, and its dysregulation can contribute to various metabolic disorders, including type 2 diabetes.
**Correct Answer:** C. Phosphofructokinase-1 (PFK-1)