18OâLabelling pattern of okadaic acid from H2 18O in dinoflagellate Prorocentrum lima elucidated by tandem mass spectrometry
2000
Izumikawa, Miho | Murata, Michio | Tachibana, Kazuo | Fujita, Tsuyoshi | Naoki, Hideo
Okadaic acid is a metabolite of the unicellular algae dinoflagellate. Its biosynthesis has attracted considerable attention since the skeletal structure was shown to be synthesized via an unprecedented route. However, its relevant intermediates or enzymes are unknown. In the course of our previous investigations on the oxygen source of okadaic acid by tandem mass spectrometry (CID MS/MS), we determined the level of 18O incorporation for each oxygen site from 18O2 and [18O2]acetate. In the present study, we examined H2 18Oâlabelling patterns of okadaic acid from dinoflagellates in comparison with salinomycin from actinomycetes and has provided intriguing information regarding biosynthesis. Unexpectedly, oxygen atoms originating from acetate were not labelled from H2 18O; this can not be accounted for by the usual metabolic route where acetylâCoA is biosynthesized via pyruvate. Similar experiments for salinomycin revealed that all of its oxygen atoms derived from acetate or propionate were labelled by H2 18O. Another interesting feature is that two oxygen sites were derived from both O2 and H2O while the others were labelled only from O2. These results imply that an oxidation mechanism other than those in actinomycetes polyethers may be involved in the biosynthesis of okadaic acid.
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