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

Fatty acid biosynthesis (FAS II)

ACP-dependent elongation using malonyl-ACP as the two-carbon donor. This alternative proposed route requires ATP for malonyl-CoA formation and a chain-length-selective termination step to release medium-chain acids.

1

Malonyl-CoA formation

acetyl-CoA + CO2 + ATP → malonyl-CoA + ADP

Enzyme: Acetyl-CoA carboxylase · EC 6.4.1.2

2

Malonyl-ACP loading

malonyl-CoA + ACP → malonyl-ACP + CoA

Enzyme: Malonyl-CoA:ACP transacylase · EC 2.3.1.39

3

Initiating condensation

acetyl-CoA + malonyl-ACP → acetoacetyl-ACP + CO2

Enzyme: 3-oxoacyl-ACP synthase III · EC 2.3.1.180

4

β-keto reduction

acetoacetyl-ACP + NADH → 3-hydroxybutyryl-ACP + NAD+

Enzyme: 3-oxoacyl-ACP reductase · EC 1.1.1.100

5

Dehydration

3-hydroxybutyryl-ACP → crotonyl-ACP + H2O

Enzyme: 3-hydroxyacyl-ACP dehydratase · EC 4.2.1.59

6

Enoyl reduction

crotonyl-ACP + NADH → butyryl-ACP + NAD+

Enzyme: Enoyl-ACP reductase I · EC 1.3.1.9

7

Further elongation and release

butyryl-ACP → hexanoyl-ACP → caproate

Enzyme: Acyl-CoA thioesterase · EC 3.1.2.20