BioChainDbA Comparative Genomics Resource for Microbial Chain Elongation and Medium Chain Fatty Acids Biosynthesis
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PATHWAY

Reverse β-oxidation (chain elongation)

CoA-dependent cyclic addition of two-carbon acetyl units. Acetyl-CoA is condensed with an acyl-CoA, reduced, dehydrated and reduced again; terminal transfer or hydrolysis releases the elongated carboxylate.

1

Acetyl-CoA condensation

2 acetyl-CoA ⇌ acetoacetyl-CoA + CoA

Enzyme: Acetyl-CoA acetyltransferase · EC 2.3.1.9

2

3-hydroxyacyl-CoA formation

acetoacetyl-CoA + NADH ⇌ 3-hydroxybutyryl-CoA + NAD+

Enzyme: 3-hydroxybutyryl-CoA dehydrogenase · EC 1.1.1.157

3

Enoyl-CoA formation

3-hydroxybutyryl-CoA ⇌ crotonyl-CoA + H2O

Enzyme: 3-hydroxybutyryl-CoA dehydratase · EC 4.2.1.55

4

Acyl-CoA reduction

crotonyl-CoA + NADH ⇌ butyryl-CoA + NAD+

Enzyme: Butyryl-CoA dehydrogenase · EC 1.3.8.1

5

Second-cycle condensation

butyryl-CoA + acetyl-CoA ⇌ 3-ketohexanoyl-CoA + CoA

Enzyme: Acetyl-CoA acetyltransferase · EC 2.3.1.9

6

Caproyl-CoA formation

3-ketohexanoyl-CoA → hexanoyl-CoA

Enzyme: 3-hydroxybutyryl-CoA dehydrogenase · EC 1.1.1.157

7

Caproate release

hexanoyl-CoA + acceptor → caproate + donor-CoA

Enzyme: CoA transferase / butyrate-acetoacetate CoA-transferase · EC 2.8.3.9