ACP is a protein that carries acyl moieties in fatty acid biosynthesis. It contains a phosphpantetheine moiety as found in coenzyme A (Figure 18.26). ACP may have a role acting as a swinging arm that carries the acyl moiety through the multiple activities of the fatty acid synthase complex.

ACP is covalently linked to acetyl-CoA and malonyl-CoA by the enzymes acetyl-CoA-ACP transacylase and malonyl-CoA-ACP transacylase, respectively.