Fatty acid synthesis
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Fatty acids are formed by the action of Fatty acid synthases from acetyl-CoA and malonyl-CoA precursors. In humans fatty acids are predominantly formed in the liver and adipose tissue, and mammary glands during lactation. Most of acetyl-CoA is formed in the mitochondria and is transported into cytosol in the form of citrate.
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[edit] Elongation
Much like β-oxidation, elongation occurs via four recurring reactions:
- Condensation
- Reduction
- Dehydration
- Reduction
In the second step of elongation, butyryl ACP condenses with malonyl ACP to form an acyl ACP compound. This continues until a C16 acyl compound is formed, at which point it is hydrolyzed by a thioesterase into palmitate and ACP.
[edit] Condensation
The first step is condensation of acetyl ACP and malonyl ACP, catalyzed by acyl-malonyl ACP condensing enzyme. This results in the formation of acetoacetyl ACP.
Although this reaction is thermodynamically unfavourable, the evolution of CO2 drives the reaction forward.
[edit] Reduction of acetoacetyl ACP
In this step, acetoacetyl ACP is reduced by NADPH into D-3-Hydroxybutyryl ACP. This reaction is catalyzed by β-Ketoacyl ACP reductase. The double bond is reduced to a hydroxyl group. Only the D isomer is formed.
[edit] Dehydration
In this reaction, D-3-Hydroxybutyryl ACP is dehydrated to crotonyl ACP. This reaction is catalyzed by 3-Hydroxyacyl ACP dehydrase.
[edit] Reduction of crotonyl ACP
During this final step, crotonyl ACP is reduced by NADPH into butyryl ACP. This reaction is catalyzed by enoyl ACP reductase.
| Lipid metabolism: lipid metabolism |
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| Fatty acid degradation (Lipolysis, Beta oxidation) - Fatty acid synthesis |
