Acyl-carrier-protein synthase transfers the 4'-phosphopantetheine moiety from coenzyme A to a Ser of an acyl-carrier-protein (PubMed:21195204). The 4'-phosphopantetheine (4'-PPT) portion of CoA provides the essential prosthetic group for a number of carrier proteins and multi-domain enzymes, priming them for the acceptance of acyl building blocks in fatty acid synthesis and many aspects of secondary metabolism mediated by polyketide synthases (PKSs) and non-ribosomal peptide synthetases (NRPSs) (PubMed:21195204). PptB is specific for the mitochondrial acyl carrier protein acpA (PubMed:21195204). apo-[ACP] + CoA = adenosine 3',5'-bisphosphate + H(+) + holo-[ACP] Essential for viability (PubMed:21195204). Leads to swollen spores in heterokaryons with a low germination rate and arrest at this stage (PubMed:21195204). Belongs to the P-Pant transferase superfamily.