Acyl Carrier Protein

Abstract

Abstract Acyl carrier protein holoprotein (holo-ACP) synthetase, an enzyme which transfers 4'-phosphopantetheine from reduced coenzyme A to acyl carrier protein apoprotein (apo-ACP) to form holo-ACP and 3',5'-adenosine diphosphate, has been shown in Escherichia coli B. At 780-fold purification the enzyme is free of apo-ACP, holo-ACP, and ACP hydrolase. The apparent Km value is 4 x 10-7 m for apo-ACP and 1.5 x 10-4 m for CoA. Dephospho-CoA and oxidized CoA are inactive as substrates. The enzyme requires Mg++ or Mn++ for activity. Both cations give complex saturation curves, with Mg++ showing substrate activation between 10-2 and 10-1 m. The holo-ACP formed in the synthetase reaction has full coenzymatic activity as measured in the malonyl-CoA-CO2 exchange reaction. Quantitative conversion of apo-ACP to holo-ACP is readily achieved with an excess of synthetase. Thus this enzyme can be utilized in an assay for apo-ACP in biological material. The reverse reaction, formation of CoA from holo-ACP and 3',5'-adenosine diphosphate, has been shown.