Farnesol and farnesal dehydrogenase(s) in corpora allata of the tobacco hornworm moth, Manduca sexta.

The metabolism of ('Hlfarnesol was studied in cell- free preparations of corpora allata from the tobacco hornworm, Manduca sexla, to assess the role of this presumed biosynthetic precursor of juvenile hormone (JH) 111. A reversed-phase ion- pair liquid chromatographic (RP-IPC) procedure was devised to separate farnesol from several potential intermediates in its presumed metabolism to JH 111: farnesal, farnesoic acid, 10,ll- epoxyfarnesoic acid, and methyl farnesoate. Following incubation of (2E,6E)-( 1 ,5,9-SH)farnesol with homogenates of corpora allata from fifth instar larvae or adult female M. sexta, and analysis by RP-IPC, the major radiolabeled products corresponded to farnesoic acid, farnesal, and a polar product(s) presumably de- rived from the tritium on C-l of farnesol. Inclusion of NAD+ in the incubations conducted with crude homogenates resulted in enhanced ('Hlfarnesol metabolism, decreased accumulation of ('Hlfarnesal, and increased levels of ('Hlfarnesoic acid. Sub- stitution of NADP+ for NAD+ was ineffective, suggesting that farnesol and/or farnesal dehydrogenase were NAD+-dependent enzymes. Pellet fractions obtained by differential centrifugation of crude homogenates exhibited both farnesol and farnesal de- hydrogenase activity but only the latter was clearly stimulated by addition of NAD'. The alcohol/aldehyde dehydrogenase(s) showed some substrate specificity for the 2E isomer; nerol and (BZ,GE)-farnesol were barely metabolized under conditions in which either geraniol or (2E,GE)-farnesol were rapidly oxidized. The identity of the ('Hlfarnesal zone obtained from RP-IPC was further established by normal-phase liquid chromatography and by gas-liquid chromatography-mass spectr0metry.l This is the first demonstration of farnesal production by insect corpora allata and provides compelling evidence for the potential in- termediacy of this compound in JH 111 biosynthesis.-Baker, F. C., B. Mauchamp, L. W. Tsai, and D. A. Schooley. Farnesol and farnesal dehydrogenase(s) in corpora allata of the tobacco hornworm moth, Manduca sexta. J. Lipid Res. 1983. 24: 1586- 1594.