Pantetheine-linked peptide intermediates in gramicidin S and tyrocidine biosynthesis

To study the function of pantetheine in gramicidin S and tyrocidine biosynthesis, pepsin digests of the polymerizing enzymes, of which only the heavy ones contain pantetheine, were analyzed. The digests of gramicidin S enzymes charged with either [(14)C]proline or with D-phenylalanyl-[(14)C]proline, were analyzed by thin-layer chromatography; only the dipeptide showed a derivative associated with pantetheine. Similar results were obtained from the heavy tyrocidine enzyme charged with either [(14)C]asparagine alone or with the pentapeptide D-Phe-Pro-Phe-D-Phe-[(14)C]Asn. Several radioactive products appeared on the thin-layer chromatograms of both these digests; association with pantetheine was found only in the case of the pentapeptide. Exposure of the chromatogram from the pentapeptide-labeled digest to performic acid and development in a second direction separated the peptide from pantetheine, indicating that a nascent peptide was originally linked to the cofactor by a thioester bond. The connection of pantetheine only with peptide residues appears to confirm its role in transpeptidation during peptide chain growth.