The invasive green alga, Caulerpa taxifolia, that has spread rapidly after its introduction into the Mediterranean and the North American Pacific, reacts to wounding by transforming its major metabolite
caulerpenyne. This
wound-activated reaction involves the transformation of the bis-enol
acetate moiety of 1, releasing reactive 1,4-dialdehydes. The ability to perform this transformation is found also in both the noninvasive Mediterranean C. prolifera and the invasive C. racemosa. Trapping experiments, as well as transformation of the model substrate
geranyl acetate, suggest that all three investigated Caulerpa spp. rely on
esterases that act upon wounding of the algae by subsequently removing the three
acetate residues of
caulerpenyne. The resulting reactive 1,4-dialdehyde oxytoxin 2 can be identified by liquid chromatography-mass spectrometry and is unstable in the wounded tissue.
Caulerpenyne transformation occurs rapidly, and severe tissue damage caused degradation of more than 50% of the stored
caulerpenyne within 1 min in all three algae. Prevention of the enzymatic reaction before extraction, by
shock freezing the tissue with liquid
nitrogen, was used for the determination of the
caulerpenyne content in intact algae. It gives about twofold higher values compared to an established
methanol extraction protocol. The speed and mechanism of the
wound-activated transformation, as well as the
caulerpenyne content in intact tissue of invasive and noninvasive Caulerpa spp., are comparable. Thus, this enzymatic transformation, despite being fast and efficient, is likely not the key for the success of the investigated invasive species.