Studies on the substrate binding sites of the pigeon liver fatty acid synthetase

Data are presented on the sites of covalent binding of acetate and malonate to the soluble pigeon liver fatty acid synthetase. Each of these compounds is bound to each of two peptide fractions which are released from the synthetase by pepsin digestion and then separated by Dowex ion-exchange chromatography. One of these peptide fractions has not been resolved. Further purification and study of the other peptide fraction has resulted in proof of the presence of 4′-phosphopantetheine bound through ester linkage to the peptide chain. In these experiments the peptides were labeled with either acetate-1- 14 C malonate-2- 14 C or pantothenic-1- 14 C acid. Quantitative analysis of the multi-enzyme complex for 4′-phosphopantetheine yielded a value close to 1 mole per mole of synthetase (450,000 gm). The implications of the findings that 1 mole of 4′-phosphopantetheine is found per mole of enzyme and that either acetate or malonate covalently bind to this compound are discussed.