Structure of one of the neuropeptides of the egg-laying hormone precursor of Lymnaea.

The neurosecretory caudo-dorsal of the freshwater pulmonate snail Lymnaea stagnalis, a peptidergic system controlling egg laying and egg-laying behavior, produce several neuropeptides. One of these peptides, calfluxin, causes the influx of Ca2+ into the albumen gland, a female sex gland of the snail. In the present study calfluxin was purified and the amino acid composition was determined. The ratio of the amino acids appeared to be very close to that of one of the predicted peptides present on the egg-laying hormone precursor of Lymnaea. This peptide was synthesized and shows a clear biological activity in the bioassay. Furthermore, it shows a chromatographic behavior similar to that of the natural peptide. Based on these evidences it is concluded that the sequence of calfluxin is: Arg-Val-Asp-Ser-Ala-Asp-Glu-Ser-Asn-Asp-Asp-Gly-Phe-Asp. Calfluxin shows a remarkable homology with the sequence of one of the predicted peptides on the egg-laying hormone precursor of the marine opisthobranch Aplysia californica.