Hepatic enzyme undergoes phosphorylation from the dephosphorylated state. Which of the following is true?
**Core Concept**
The question is testing the understanding of the regulation of hepatic enzymes, specifically the role of phosphorylation in their activation. Phosphorylation is a post-translational modification that can either activate or inhibit enzymes, depending on the enzyme and the context. In the case of hepatic enzymes, phosphorylation is often used to regulate their activity in response to changes in the body's metabolic state.
**Why the Correct Answer is Right**
The correct answer involves the enzyme phosphoenolpyruvate carboxykinase (PEPCK), which is a key enzyme in gluconeogenesis. PEPCK is activated by dephosphorylation, not phosphorylation. This is because the dephosphorylated state of PEPCK allows it to bind to its substrate, phosphoenolpyruvate, and initiate the gluconeogenic pathway. The phosphorylated form of PEPCK is the inactive state, which is maintained by the action of a specific protein phosphatase. The correct answer, therefore, involves the role of dephosphorylation in activating PEPCK.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it is not specific to the regulation of hepatic enzymes or the role of phosphorylation in their activity.
* **Option B:** This option is incorrect because it does not accurately describe the regulation of PEPCK or any other hepatic enzyme.
* **Option D:** This option is incorrect because it is not relevant to the regulation of hepatic enzymes or the role of phosphorylation in their activity.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that phosphorylation is often used to regulate the activity of enzymes, and the dephosphorylated state is often the active form. This is particularly important in the context of gluconeogenesis, where the activation of PEPCK is critical for the production of glucose.
**Correct Answer:** C.