Enzyme inhibited by insulin ?
**Core Concept**
Insulin is a hormone that plays a crucial role in glucose metabolism by facilitating the uptake of glucose into cells. To exert its effects, insulin activates various intracellular signaling pathways, including the inhibition of key enzymes involved in glucose production and glycogenolysis.
**Why the Correct Answer is Right**
The correct answer is related to the enzyme phosphoenolpyruvate carboxykinase (PEPCK), which is involved in gluconeogenesis, the process of generating glucose from non-carbohydrate sources. Insulin inhibits PEPCK by phosphorylating and thus inactivating the enzyme, thereby reducing glucose production in the liver. This effect is mediated through the insulin signaling pathway, which activates phosphatidylinositol 3-kinase (PI3K) and protein kinase B (Akt), leading to the inhibition of PEPCK.
**Why Each Wrong Option is Incorrect**
**Option A:** Glucagon is not inhibited by insulin; rather, insulin counteracts the effects of glucagon, which promotes glucose production.
**Option B:** Pyruvate kinase is actually activated by insulin, not inhibited, as part of the insulin signaling pathway that promotes glycolysis.
**Option C:** Glycogen synthase is activated by insulin, not inhibited, as part of the insulin signaling pathway that promotes glycogen synthesis.
**Clinical Pearl / High-Yield Fact**
Insulin's inhibitory effect on PEPCK highlights the importance of insulin in regulating glucose metabolism and maintaining normoglycemia. This understanding is critical for managing diabetes mellitus and other metabolic disorders.
**Correct Answer: D. Phosphoenolpyruvate carboxykinase**