The structure of ubiquinones isolated from developing embryos of Manduca sexta

Like many other lepidoptera, Manduca sexta synthesizes juvenile hormones (JH) that differ from classic isoprenoids by having one or more ethyl, instead of methyl, branches attached to the hydrocarbon chain. This difference originates from the utilization of homomevalonate in the place of mevalonate for synthesis of the different forms of JH. No other ethyl- branched homoisoprenoid has been found in lepidopteran insects. We reported earlier that only methyl-branched dolichols were detected in M. sexta larvae. We have now isolated ubiquinones from the embryos of M. sexta and then analyzed them by chemical ionization mass spectrometry. No ubiquinone homologue with an ethyl-branched side chain was detected. The predominant homologue found is ubiquinone Q-9 entirely with methyl-branches, with only a trace amount of ubiquinone Q-10. These results suggest that JH are synthesized by specialized enzymatic mechanisms in the corpora allata, while other major isoprenoids are synthesized by the more common enzymes present in eukaryotic systems.