Insulin increases the activities of all of the following enzymes, EXCEPT:
**Core Concept**
Insulin is a hormone with anabolic effects, promoting glucose uptake and storage, and influencing various metabolic pathways. It activates several enzymes involved in glycogen synthesis, lipid synthesis, and protein synthesis.
**Why the Correct Answer is Right**
Insulin stimulates the activity of several key enzymes involved in glucose metabolism, including glycogen synthase, pyruvate dehydrogenase, and acetyl-CoA carboxylase. Glycogen synthase, in particular, is crucial for glycogen synthesis, catalyzing the transfer of glucose units from UDP-glucose to the growing glycogen chain. Insulin also activates pyruvate dehydrogenase, which converts pyruvate to acetyl-CoA, facilitating the entry of glucose into the citric acid cycle.
**Why Each Wrong Option is Incorrect**
* **Option A:** Phosphofructokinase-2 (PFK-2) is an enzyme involved in the regulation of glycolysis, but insulin actually decreases its activity to inhibit glycolysis.
* **Option B:** Glucagon is a hormone that has the opposite effect of insulin on glucose metabolism. Glucagon increases the activity of enzymes involved in glycogen breakdown, such as glycogen phosphorylase.
* **Option C:** Hexokinase is an enzyme involved in the first step of glycolysis, but insulin's effect on hexokinase is not as significant as its effect on other enzymes involved in glucose metabolism.
**Clinical Pearl / High-Yield Fact**
Insulin's anabolic effects are essential for maintaining glucose homeostasis and preventing hyperglycemia. Understanding the mechanisms by which insulin regulates enzyme activity is crucial for managing diabetes and other metabolic disorders.
**Correct Answer:** A. Phosphofructokinase-2 (PFK-2).