Palmitate is synthesized by stepwise condensation of C2 units to a growing acyl chain. Each elongation cycle results in the addition of two carbons to the acyl chain, and consists of four separate reactions. The pathway starts with acetyl-CoA interacting with hydrogen carbonate through an ATP driven acetyl-CoA carboxylase resulting in a phosphate, an ADP , a hydrogen ion and a malonyl-CoA. The latter compound interacts with a holo-[acp] through a malonyl-CoA-ACP transacylase resulting in a CoA and a malonyl-[acp]. This compound interacts with hydrogen ion, acetyl-CoA through a KASIII resulting in a CoA, carbon dioxide and an acetoacetyl-[acp]. The latter compound interacts with a hydrogen ion through a NADPH driven 3-oxoacyl-[acyl-carrier-protein] reductase resulting in an NADP and a (R) 3-Hydroxybutanoyl-[acp](1). This compound is then dehydrated by a 3-hydroxyacyl-[acyl-carrier-protein] dehydratase resulting in the release of water and a crotonyl-[acp](2). The crotonyl-[acp] interacts with a hydrogen ion through a NADH enoyl-[acyl-carrier-protein] reductase(NAD) resulting in NAD and a butyryl-[acp](3). The butyryl-[acp] interacts with a hydrogen ion, a malonyl-[acp] through a KASI resulting in a holo-[acp],carbon dioxide and a 3-oxo-hexanoyl-[acp](4). The 3-oxo-hexanoyl-[acp] interacts with a hydrogen ion through a NADPH driven 3-oxoacyl-[acyl-carrier-protein] reductase resulting in an NADP and a (R) 3-Hydroxyhexanoyl-[acp](1). This compound is then dehydrated by a 3-hydroxyacyl-[acyl-carrier-protein] dehydratase resulting in the release of water and a trans hex-2-enoyl-[acp](2). The trans hex-2-enoyl-[acp] interacts with a hydrogen ion through a NADH enoyl-[acyl-carrier-protein] reductase(NAD) resulting in NAD and a hexanoyl-[acp](3). The hexanoyl-[acp] interacts with a hydrogen ion, a malonyl-[acp] through a KASI resulting in a holo-[acp],carbon dioxide and a 3-oxo-octanoyl-[acp](4). The 3-oxo-octanoyl-[acp] interacts with a hydrogen ion through a NADPH driven 3-oxoacyl-[acyl-carrier-protein] reductase resulting in an NADP and a (R) 3-Hydroxyoctanoyl-[acp](1). This compound is then dehydrated by a 3-hydroxyacyl-[acyl-carrier-protein] dehydratase resulting in the release of water and a trans oct-2-enoyl-[acp](2). The trans oct-2-enoyl-[acp] interacts with a hydrogen ion through a NADH enoyl-[acyl-carrier-protein] reductase(NAD) resulting in NAD and a octanoyl-[acp](3). The octanoyl-[acp] interacts with a hydrogen ion, a malonyl-[acp] through a KASI resulting in a holo-[acp],carbon dioxide and a 3-oxo-decanoyl-[acp](4). The 3-oxo-decanoyl-[acp] interacts with a hydrogen ion through a NADPH driven 3-oxoacyl-[acyl-carrier-protein] reductase resulting in an NADP and a (R) 3-Hydroxydecanoyl-[acp](1). This compound is then dehydrated by a 3-hydroxyacyl-[acyl-carrier-protein] dehydratase resulting in the release of water and a trans-delta2-decenoyl-[acp](2). The a trans-delta2-decenoyl-[acp] interacts with a hydrogen ion through a NADH enoyl-[acyl-carrier-protein] reductase(NAD) resulting in NAD and a decanoyl-[acp](3). The decanoyl-[acp] interacts with a malonyl-[acp] through a KASI resulting in a holo-[acp],carbon dioxide and a 3-oxo-dodecanoyl-[acp](4). The 3-oxo-dodecanoyl-[acp ]interacts with a hydrogen ion through a NADPH driven 3-oxoacyl-[acyl-carrier-protein] reductase resulting in an NADP and a (R) 3-Hydroxydodecanoyl-[acp](1). This compound is then dehydrated by a 3-hydroxyacyl-[acyl-carrier-protein] dehydratase resulting in the release of water and a trans dodec-2-enoyl-[acp](2). The trans dodec-2-enoyl-[acp] interacts with a hydrogen ion through a NADH enoyl-[acyl-carrier-protein] reductase(NAD) resulting in NAD and a dodecanoyl-[acp](3). This compound can either react with water spontaneously resulting in a hydrogen ion, a holo-[acp] and a dodecanoic acid or it interacts with a hydrogen ion, a malonyl-[acp] through a KASI resulting in a holo-[acp],carbon dioxide and a 3-oxo-myristoyl-[acp](4). The 3-oxo-myristoyl-[acp] interacts with a hydrogen ion through a NADPH driven 3-oxoacyl-[acyl-carrier-protein] reductase resulting in an NADP and a (3R) 3-Hydroxymyristoyl-[acp](1). This compound is then dehydrated by a 3-hydroxyacyl-[acyl-carrier-protein] dehydratase resulting in the release of water and a trans tetradec-2-enoyl-[acp](2). This compound interacts with a hydrogen ion, through a NADH-driven KASI resulting in a NAD and a myristoyl-[acp]. Myristoyl-[acp] with a hydrogen ion, a malonyl-[acp] through a KASI resulting in a holo-[acp],carbon dioxide and a 3-oxo-palmitoyl-[acp](4). The 3-oxo-palmitoyl-[acp] interacts with a hydrogen ion through a NADPH driven 3-oxoacyl-[acyl-carrier-protein] reductase resulting in an NADP and a (3R) 3-Hydroxypalmitoyl-[acp](1). This compound is then dehydrated by a 3-hydroxyacyl-[acyl-carrier-protein] dehydratase resulting in the release of water and a trans hexadecenoyl-[acp](2). The trans hexadecenoyl-[acp] interacts with a hydrogen ion through a NADH enoyl-[acyl-carrier-protein] reductase(NAD) resulting in NAD and a palmitoyl-[acp](3). Palmitoyl then reacts with water spontaneously resulting in a hydrogen ion, a holo-[acp] and palmitic acid. No integral membrane protein required for long chain fatty acid uptake has been identified in E. coli. The transport of long chain fatty acids across the cytoplasmic membrane is dependent on fatty acyl-CoA synthetase. An energised membrane is necessary for fatty acid transport and it has been suggested that uncharged fatty acids flip across the inner membrane by diffusion.

Palmitate Biosynthesis 2 References