High-yielding strains of Claviceps purpurea (Fr.) Tul, grown on a defined medium, have been used for a study of the biosynthesis of the peptide ergot alkaloid, ergotamine. l -[U- 14 C]tryptophan, dl -[2- 14 C]mevalonic acid lactone, sodium [2- 14 C]acetate, sodium [ 14 C]formate and the methyl group of l -[ methyl - 14 C]methionine were efficiently incorporated into the peptide alkaloids and specifically labelled the ergoline moiety of ergotamine. These results are the same as previously found for the biosynthesis of other ergot alkaloids. Time-course incubation experiments demonstrated that l -[U- 14 C]phenylalanine, l -[U- 14 C]proline and l -[U- 14 C]alanine were incorporated into the peptide ergot alkaloids. Chemical degradation of the radioactive alkaloid derived from additional precursor incubation experiments showed that phenylalanine and proline function as the most efficient precursors, and specifically label the constitutive side-chain phenylalanyl and prolyl moieties of the alkaloid. The evidence obtained from l -[U- 14 C]alanine-incorporation experiments was inconclusive. However, degradation of ergotamine isolated after incubation with dl -[1- 14 C]alanine, showed that the carboxyl group of the labelled amino acid was specifically incorporated into the α-hydroxy-α-amino acid residue of the alkaloid. This, in conjunction with the l -[U- 14 C]alanine-incorporation results, showed conclusively that all three carbon atoms of alanine were incorporated as a biosynthetic unit into the α-hydroxy-α-amino acid moiety of ergotamine.
1. The biosynthetic origin of the amide substituent of N -(α-hydroxyethyl)lysergamide has been studied. 2. [1- 14 C]Acetate, [ 14 C]formate, [2- 14 C]mevalonic acid lactone, [2- 14 C]indole, dl -[3- 14 C]tryptophan, dl -[3- 14 C]serine, dl -[2- 14 C]alanine and [2- 14 C]pyruvate were efficiently incorporated into the alkaloid, but not dl -[1- 14 C]alanine or [1- 14 C]pyruvate. 3. Only the dl -[2- 14 C]alanine- and [2- 14 C]pyruvate-derived alkaloid contained appreciable radioactivity in the amide substituent. 4. l -[ 15 N]Alanine-derived alkaloid was shown to be specifically labelled in the amide nitrogen. However, l -[ 14 C, 15 N]alanine was found to be incorporated into the methylcarbinolamide substituent with an appreciable increase in the 15 N/ 14 C ratio, suggesting that alanine is not the direct precursor of this moiety.