Acyl Carrier Protein

Acyl carrier protein hydrolase, a phosphodiesterase which catalyzes the hydrolysis of Escherichia coli acyl carrier protein to yield the prosthetic group and the apoprotein, was purified do-fold from extracts of E. coli.Hydrolysis of acyl carrier protein by this enzyme requires manganese (or other divalent cations) and it is stimulated by sulfhydryl compounds such as dithiothreitol or 2-mercaptoethanol.The enzymatic reaction products are 4'-phosphopantetheine and the apoprotein which was isolated and identified by comparison of its molecular weight and amino acid composition to intact acyl carrier protein.Acyl carrier protein hydrolase is very specific in regard to substrate since it does not catalyze the hydrolysis of 4'-phosphopantetheine from large peptides of E. coli acyl carrier protein.It does, however, catalyze the cleavage of 4'-phosphopantetheine from E. coli acetyl acyl carrier protein and from Clostridium bufyricum acyl carrier protein.Recent studies have indicated that acyl carrier protein rather than coenzyme A is involved in a number of biosynthetic reactions (2-7).Investigations of the mechanism of ACPi involvement in fatty acid synthesis de novo have shown the critical role of this protein in this sequence of reactions (8-13).ACP is a conjugated protein consisting of apoprotein and a prosthetic group, 4'-phosphopantetheine, which is bound through phosphodiester linkage to the hydroxyl group of a serine residue of the protein.Fatty acid synthesis in E. coli occurs with all the substrates linked as thioesters to the sulfhydryl group of 4'phosphopantetheine.Further studies have been initiated to investigate the mechanism of ACP synthesis and the regulation of cellular ACP concentration.This report describes partial purification and properties of an enzyme, ACP hydrolase, which catalyzes the cleavage of ACP to form 4'-phosphopantetheine and a protein which has been identified as ACP apoprotein.