Which of the following activates acetyl-CoA carboxylase?

Question

BlackTom AI · Accepted Answer

Acetyl-CoA carboxylase (ACC) catalyzes the committed, rate‑limiting step of fatty acid synthesis: acetyl‑CoA + CO2 + ATP → malonyl‑CoA + ADP + Pi (biotin is the CO2 carrier). ACC activity is controlled by hormonal signals and allosteric effectors to match fed/fasting and energy states.

Relevant knowledge points and concepts:
- Hormonal regulation: Insulin signals the fed state and promotes anabolic processes (glycogen and fatty acid synthesis). Glucagon and epinephrine signal fasting/stress and activate catabolic pathways.
- Covalent modification: ACC is active when dephosphorylated and inactive when phosphorylated. Insulin stimulates protein phosphatases (e.g., PP2A) that dephosphorylate and activate ACC. Glucagon/epinephrine activate adenylate cyclase → cAMP → PKA, which phosphorylates and inhibits ACC.
- Energy sensing: AMP‑activated protein kinase (AMPK) is activated when cellular AMP is high (low energy); AMPK phosphorylates and inhibits ACC.
- Allosteric control: Citrate allosterically activates ACC (promotes polymerization/active form); long‑chain acyl‑CoAs inhibit it.

Step‑by‑step reasoning:
1. ACC must be active in the fed state to generate malonyl‑CoA for fatty acid synthesis.
2. Insulin is the principal fed‑state hormone; it activates protein phosphatases that remove inhibitory phosphate groups on ACC.
3. Dephosphorylated ACC adopts the active polymeric form and, together with citrate activation, increases malonyl‑CoA production.
4. By contrast, epinephrine and glucagon trigger PKA and lead to ACC phosphorylation (inactivation). AMPK, activated by high AMP, also phosphorylates and inhibits ACC.

Why the correct answer is correct:
- Insulin directly promotes ACC activation via dephosphorylation and signaling that favors fatty acid synthesis in the fed state.

Why the other options are incorrect:
- Epinephrine: activates PKA → phosphorylates/inhibits ACC.
- Glucagon: same pathway as epinephrine → inhibits ACC.
- AMPK: energy sensor that phosphorylates and inhibits ACC when cellular energy is low.

Conclusion: ACC is activated by insulin; therefore the correct choice is a. Insulin, matching the provided answer.

Which of the following activates acetyl-CoA carboxylase?单项选择题

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