One-step purification and properties of a two-peptide fatty acid synthetase from the uropygial gland of the goose

Abstract

Cell-free extracts from the uropygial gland of goose catalyzed the incorporation of malonyl-CoA into normal fatty acids and methylmalonyl-CoA into multimethyl branched acids with NADPH as the preferred reductant. Purification of fatty acid synthetase from this extract was accomplished in 1 step by gel filtration with Sepharose 4B. Homogeneity of the fatty acid synthetase was shown by analytical ultracentrifugation, immunodiffusion assays, polyacrylamide disc gel electrophoresis and sodium dodecyl sulfate polyacrylamide disc gel electrophoresis. At a pH of 7.0, apparent Km values of 3.6 .times. 10-5 M and 1.5 .times. 10-5 M were calculated for malonyl-CoA and NADPH, respectively. The major products synthesized by the enzyme from malonyl-CoA and methylmalonyl-CoA were free hexadecanoic acid and free 2,4,6,8-tetramethyldecanoic acid, respectively, with acetyl-CoA as primer. A MW value of 547,000 was determined for the goose fatty acid synthetase by sedimentation equilibrium centrifugation. The purified enzyme had an s20,w of 13.5 S and was partially dissociated in low-ionic strength buffer into a 9.3S species, and this dissociation was accompanied by a corresponding partial inactivation of the enzymatic activity. Reassociation and reactivation of the partially dissociated fatty acid synthetase were accomplished in either 0.2 M KCl or 200 .mu.M NADPH. These properties of the goose enzyme are similar to those of other animal fatty acid synthetases, as was the amino acid composition. Dissociation of the purified enzyme with sodium dodecyl sulfate resulted in only 2 equal MW polypeptides (269,000), as determined by sodium dodecyl sulfate polyacrylamide disc gel electrophoresis. Injection of labeled pantothenic acid into the uropygial gland resulted in the synthesis of labeled fatty acid synthetase in which the label appeared to be located exclusively in the 4''-phosphopantotheine moiety. Analysis of the labeled enzyme by gel filtration and polyacrylamide disc gel electrophoresis in the presence of sodium dodecyl sulfate showed that the labeled pantothenate was contained exclusively in the half molecular weight moiety. The enzyme contained one 4''-phosphopantetheine residue/subunit (269,000), as determined by measurement of the taurine generated by hydrolysis of performic acid-treated enzyme. Sodium dodecyl sulfate-activated proteolytic activity was associated with goose fatty acid synthetase, and this proteolysis resulted in the formation of small-MW protein fragments (< 200,000) during treatment of the enzyme with sodium dodecyl sulfate. This proteolysis could be prevented by diisopropyl fluorophosphate and p-chloromercuribenzoate. The goose uropygial gland fatty acid synthetase consists of 2 multifunctional polypeptide subunits, each containing 1 covalently linked 4''-phosphopantetheine.