Biosynthesis of Tiglic, Ethacrylic, and 2-Methylbutyric Acids in a Carabid Beetle, Pterostichus (Hypherpes) californicus
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Tiglic, 2-methylbutyric, and ethacrylic acids are found in the pygidial gland defensive fluid of many carabid beetles. By injecting a deuterium-labeled precursor into the carabid beetle Pterostichus (Hypherpes) californicus, and analyzing the defensive fluid by gas chromatography/mass spectrometry, we were able to demonstrate that tiglic and ethacrylic acids are biosynthesized from isoleucine via 2-methylbutyric acid. Moreover, we observed that the injection of l-isoleucine induces an increased production of tiglic acid in P. californicus. A strong primary kinetic isotope effect was found to operate in the dehydrogenation step of 2-methylbutyric acid to tiglic and ethacrylic acids. Consequently, ethacrylic acid was found to preferentially accumulate the deuterium labeling from [2,3,4,4-2H4]isoleucine during our biosynthetic experiments.
KeywordsBiosynthesis Defensive allomones Tiglic acid 2-Methylbutyric acid Ethacrylic acid Isoleucine Carabid beetles Pterostichus (Hypherpes) californicus Carabidae
The authors wish to thank Stevens Institute of Technology for financial support, and Aman Gill, UC, Berkeley, for assistance with handling and caring of beetle cultures. This research was funded (in part) by the United States Department of Agriculture, Cooperative State Research, Education, and Extension Service in partnership with the California State Agricultural Experiment Station.
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