In enzymology and molecular biology, a holo-[acyl-carrier-protein] synthase (ACPS, EC 2.7.8.7) is an enzyme that catalyzes the chemical reaction: This enzyme belongs to the family of transferases, specifically those transferring non-standard substituted phosphate groups.

It transfers a 4'-phosphopantetheine (4'-PP) moiety from coenzyme A (CoA) to an invariant serine in an acyl carrier protein (ACP), a small protein responsible for acyl group activation in fatty acid biosynthesis.

This post-translational modification renders holo-ACP capable of acyl group activation via thioesterification of the cysteamine thiol of 4'-PP.

The most highly conserved regions of the protein are involved in binding the magnesium ion.

As of late 2007, 8 structures have been solved for this class of enzymes, with PDB accession codes 1F7L, 1F7T, 1F80, 1FTE, 1FTF, 1FTH, 2JBZ, and 2JCA.