Acetyl-CoA carboxylase

Definition

Acetyl-CoA carboxylase is an enzyme that plays a crucial role in fatty acid synthesis by catalyzing the conversion of acetyl-CoA into malonyl-CoA, a key building block in lipid metabolism. This enzyme acts as a regulatory point, linking carbohydrate and lipid metabolism by responding to various signals, thus influencing energy storage and utilization in cells.

5 Must Know Facts For Your Next Test

1. Acetyl-CoA carboxylase is activated by citrate, indicating high energy availability and promoting fatty acid synthesis.
2. The enzyme is inhibited by long-chain fatty acyl-CoAs, which signals sufficient fatty acid levels and reduces further synthesis.
3. Acetyl-CoA carboxylase exists in two isoforms: ACC1, predominantly found in lipogenic tissues, and ACC2, which is more prevalent in muscle tissues.
4. Regulation of this enzyme is crucial because it determines whether excess carbohydrates are converted into fats for storage or utilized for energy.
5. The activity of acetyl-CoA carboxylase is influenced by hormonal signals such as insulin, which promotes its activity, while glucagon has the opposite effect.

Review Questions

• How does acetyl-CoA carboxylase link carbohydrate metabolism to lipid synthesis?
  • Acetyl-CoA carboxylase connects carbohydrate metabolism to lipid synthesis by converting acetyl-CoA, derived from glucose breakdown, into malonyl-CoA, which is essential for building fatty acids. When carbohydrates are abundant, this enzyme promotes the storage of excess energy as fat. Therefore, it serves as a critical regulatory step that balances energy production and storage based on nutrient availability.
• Discuss the regulatory mechanisms that control the activity of acetyl-CoA carboxylase in response to hormonal signals.
  • Acetyl-CoA carboxylase is regulated by several hormones that affect its activity based on the body's energy status. Insulin enhances its activity through dephosphorylation, promoting fatty acid synthesis when glucose levels are high. In contrast, glucagon activates AMP-activated protein kinase (AMPK), leading to phosphorylation and inhibition of the enzyme when energy levels are low. This regulation ensures that lipid synthesis occurs only when energy is plentiful.
• Evaluate the implications of dysregulation of acetyl-CoA carboxylase in metabolic disorders such as obesity and diabetes.
  • Dysregulation of acetyl-CoA carboxylase can lead to excessive fatty acid synthesis and storage, contributing to obesity and insulin resistance. In conditions like metabolic syndrome, where there is an imbalance between energy intake and expenditure, increased activity of this enzyme can promote the accumulation of lipids in tissues, exacerbating insulin resistance. Understanding this relationship provides insights into potential therapeutic targets for managing metabolic disorders by modulating this enzyme's activity to restore metabolic balance.

Related terms

Malonyl-CoA: A three-carbon molecule formed from acetyl-CoA by the action of acetyl-CoA carboxylase, essential for fatty acid synthesis.

Fatty Acid Synthase: An enzyme complex that catalyzes the synthesis of fatty acids from malonyl-CoA and other substrates, functioning downstream of acetyl-CoA carboxylase.

AMP-activated Protein Kinase (AMPK): An enzyme that plays a key role in cellular energy homeostasis by phosphorylating and inhibiting acetyl-CoA carboxylase when cellular energy levels are low.