Acetyl CoA Carboxylase

Definition

Acetyl CoA carboxylase is a critical enzyme that catalyzes the rate-limiting step in the biosynthesis of fatty acids. It is responsible for the conversion of acetyl-CoA into malonyl-CoA, which serves as the two-carbon building block for the elongation of fatty acid chains.

5 Must Know Facts For Your Next Test

1. Acetyl CoA carboxylase is the rate-limiting enzyme in the biosynthesis of fatty acids, catalyzing the conversion of acetyl-CoA to malonyl-CoA.
2. Malonyl-CoA is the two-carbon building block used for the elongation of fatty acid chains during fatty acid synthesis.
3. The activity of acetyl CoA carboxylase is tightly regulated by allosteric effectors, such as citrate (activator) and AMP (inhibitor), as well as covalent modification via phosphorylation.
4. Phosphorylation of acetyl CoA carboxylase by AMP-activated protein kinase (AMPK) leads to its inactivation, reducing fatty acid synthesis and promoting fatty acid oxidation.
5. Acetyl CoA carboxylase is a biotin-dependent enzyme, with biotin serving as a cofactor in the carboxylation reaction.

Review Questions

• Explain the role of acetyl CoA carboxylase in the biosynthesis of fatty acids.
  • Acetyl CoA carboxylase catalyzes the rate-limiting step in fatty acid synthesis by converting acetyl-CoA into malonyl-CoA, which serves as the two-carbon building block for the elongation of fatty acid chains. This enzyme is critical for the de novo synthesis of fatty acids, as malonyl-CoA is the substrate for the fatty acid synthase complex that progressively adds two-carbon units to the growing fatty acid chain.
• Describe the regulatory mechanisms that control the activity of acetyl CoA carboxylase.
  • The activity of acetyl CoA carboxylase is tightly regulated through both allosteric and covalent mechanisms. Allosteric regulation involves the binding of activators, such as citrate, which increases the enzyme's affinity for its substrates. Conversely, AMP acts as an allosteric inhibitor, decreasing the enzyme's activity. Covalent regulation occurs through the phosphorylation of acetyl CoA carboxylase by AMP-activated protein kinase (AMPK), which inactivates the enzyme and reduces fatty acid synthesis, promoting fatty acid oxidation instead.
• Analyze the significance of the regulation of acetyl CoA carboxylase in the context of cellular energy homeostasis and metabolic adaptation.
  • The regulation of acetyl CoA carboxylase plays a crucial role in maintaining cellular energy homeostasis and facilitating metabolic adaptation. When cellular energy levels are high, as indicated by elevated citrate and low AMP levels, acetyl CoA carboxylase is activated, promoting fatty acid synthesis and storage of excess energy in the form of triglycerides. Conversely, when energy levels are low and AMP is elevated, AMPK phosphorylates and inactivates acetyl CoA carboxylase, reducing fatty acid synthesis and instead promoting the oxidation of fatty acids to generate ATP and restore energy balance. This dynamic regulation of acetyl CoA carboxylase allows the cell to adjust its metabolic pathways in response to changing energy demands.

Related terms

Fatty Acid Synthesis:

The metabolic pathway that produces long-chain fatty acids from acetyl-CoA and NADPH, regulated by acetyl CoA carboxylase.

Malonyl-CoA: The product of the acetyl CoA carboxylase reaction, which provides the two-carbon units for fatty acid chain elongation.

Regulation of Acetyl CoA Carboxylase: The allosteric and covalent mechanisms that control the activity of acetyl CoA carboxylase, including the effects of citrate, AMP, and phosphorylation.