Acyl carrier protein. XI. The specificity of acyl carrier protein synthetase.

Abstract Holo acyl carrier protein synthetase transfers 4'-phosphopantetheine from reduced coenzyme A to acyl carrier protein (ACP) apoprotein to form ACP holoprotein (holo-ACP). The specificity of this enzyme was tested by using apopeptides derived from ACP. The apopeptides were derived from holopeptides, those containing 4'-phosphopantetheine, by the mild and specific action of 60% hydrofluoric acid. Holo-ACP, when treated with 60% HF, yielded ACP apoprotein (apo-ACP) which was completely converted to holo-ACP by the action of holo-ACP synthetase. In addition the optical rotatory dispersion curves for apo- and holo-ACP are quite similar, further supporting the contention that 60% HF treatment causes little or no structural damage to apo-ACP. Apopeptides consisting of Residues 7 through 77 or 19 through 61 were inactive with the enzyme. The corresponding holopeptides are also inactive in fatty acid synthesis. Apopeptide 1 through 74 is readily converted to holopeptide which is fully active in fatty acid synthesis. It is concluded that the same site (or sites) and structure of ACP are critical in interactions with enzymes of fatty acid biosynthesis or with enzymes involved in the addition and removal of the prosthetic group.