-!- All polyketide synthases, fatty-acid synthases and non-ribosomal peptide synthases require post-translational modification of their constituent acyl-carrier-protein (ACP) domains to become catalytically active. -!- The inactive apo-proteins are converted into their active holo-forms by transfer of the 4'-phosphopantetheinyl moiety of CoA to the sidechain hydroxy group of a conserved serine residue in each ACP domain. -!- The enzyme from human can activate both the ACP domain of the human cytosolic multifunctional fatty acid synthase and that associated with human mitochondria as well as peptidyl-carrier and acyl-carrier- proteins from prokaryotes. -!- Removal of the 4-phosphopantetheinyl moiety from holo-ACP is carried out by EC 3.1.4.14.