How to Produce a Chemical Defense: Structural Elucidation and Anatomical Distribution of Aplysioviolin and Phycoerythrobilin in the Sea Hare Aplysia californica

Abstract

We previously used bioassay-guided fractionation to identify phycoerythrobilin (1) and its monomethyl ester, aplysioviolin (2), as components in the ink secretion of a marine gastropod, the sea hare Aplysia californica, that act as chemical deterrents against predatory blue crabs. This was the first report of 1 as a natural product. Compound 2 was previously reported as a natural product from three species of Aplysia (A. fasciata, A. dactylomela, and A. parvula), but the reported structure and composition of stereoisomers of 2 are different among these species. Sea hares are thought to produce 2 from phycoerythrin, a photosynthetic pigment in their red-algal diet composed of a phycobiliprotein covalently linked to the chromophore 1, by cleavage of the covalent bond and methylation of 1, but neither the sequence nor the anatomical location of the cleavage and methylation is known. In this study, we clarify the structure of 1 and 2 in ink secretion of A. californica, and describe the distribution of 1 and 2 in the tissues of sea hares. We conclude that cleavage of the covalent bond in phycoerythrin occurs first, forming 1 in the digestive gland, followed by methylation of 1 to yield 2 in the ink gland.

Taste-mediated behavioral and electrophysiological responses by the predatory fish Ariopsis felis to deterrent pigments from Aplysia californica ink

“…The ink of sea hares and two of ink's major components, APV and PEB (Kamio et al 2010a), are relevant and potent deterrents to sea catfish. Our behavioral studies show that sea catfish, which are sympatric to sea hares, rejected food or food-flavored pellets treated with biologically relevant concentrations of whole ink, APV, or PEB.…”

“…The relative retention times, peak heights and UV/ Visual spectra were considered sufficient for identification of APV and PEB for the purposes of analysis in this study. Kamio et al (2010a) combined NMR analysis with UV/ Visual Spectra and HPLC techniques to further study the composition of APV and PEB. Following HPLC separation, samples of the fractions containing APV and PEB were analyzed for free amino acid content (AminoAcids.com, St. Paul, MN USA), to ensure that any behavioral or electrophysiological response to these fractions was not due to free amino acids.…”

“…We used APV and PEB as natural stimuli to examine behavioral and electrophysiological responses of the sea catfish, Ariopsis felis. We selected A. felis because it is sympatric with the sea hare A. dactylomela, whose ink contains APV and PEB (Kamio et al 2010a), and because the organization of the gustatory pathways and how they process some foodrelated attractants (i.e. amino acids) has already been characterized in some detail (Michel and Caprio 1991;Michel et al 1993;Kohbara and Caprio 1996;reviewed in Caprio and Derby 2008).…”

Oesophageal chemoreceptors of blue crabs,Callinectes sapidus, sense chemical deterrents and can block ingestion of food

“…In our own experiments leading to this paper, we found that compounds such as capsaicin, menthol, allyl isothiocyanate and Nmethylmaleimide, which are known irritants and deterrents, were almost insoluble in ASW and were not pursued further because they tended to aggregate in big clumps, making it impossible for us to deliver them consistently (data not shown). Interestingly, although PEB and APV are equally potent, A. californica transforms the former into the latter by changing a carboxyl group into a methyl ester (Kamio et al, 2010b), a reaction that may make the molecule even less soluble in water.…”

Applications of Natural Purple from <i>Dolabella </i><i>au</i><i>ricularia</i>: Colouration of Cholesteric Liquid Crystals

“…Dolabella auricularia collects molecules from the sea weeds in the sea and stores the compounds. Secretion of the ink from dolabella auricularia contains several molecules, such as aplysioviolin [4], dolabellin [5,6], auriside A and dolastatin 10 [7] (Figure 5). In the case of auriside A, synthesis of C1-C9 of the molecule was carried out with Meinwald reaction of alkyl propionate [8].…”