Physiological and biochemical study of D-amino acid-containing peptide, fulicin and fulyal originated from molluscs

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(1) Degradation enzyme of fulicin and fulyalAn endopeptidase-like activity was observed when fulicin and fulyal were incubated with the membrane fraction prepared from the subesophageal ganglia of Achatina fulica. The presence of bivalent metal ion and inhibition by specific inhibitors revealed that this activity was attributed to an endopeptidase 24.1.1-like enzyme.(2) Expressions of achatin-I, fulicin, fulyal and ACEP-I (Achatina cardioexcitatory peptide-I)Expressions of precursor cDNAs of achatin-I, fulicin, fulyal and ACEP-I were examined in the central ganglia and the artria of Achatina fulica. Achatin-I cDNA was detected in the subesophageal ganglia, but not in the artria. Precursor cDNAs of fulicin, fulyal, and ACEP-I were observed from both the subesophageal ganglia and the atria. ACEP-I cDNA was also found in the cerebral ganglia. In situ hybridization experiments revealed that achatin-I transcripts were expressed in neurons of pedal ganglia, fulicin and fulyal transcripts were found in those of parietal ganglia, ACEP-I transcripts were detected in those of cerebral and pedal ganglia. From these results, achatin-I was synthesized in neurons of pedal ganglia ; on the other hand fulicin, fulyal, and ACEP-I were produced from both the central ganglia and the atria, and might be artrial hormone-like peptides.(3) Roles of fulicin and fulyal on the reproductive organs of Achatina fulicaFulicin has been thought to control male copulatory behavior in Achatina fulica. The vagina and the oviduct of the snail were densely innervated by fulicin-like immunoreactive neuronal fibers. Fulicin was actually present in the vagina by mass spectrometry analysis. Fulicin showed potent excitatory effect on contractions of the vagina and the oviduct. These results suggest that fulicin controls female egg-laying behavior as an excitatory neuropeptide regulating the female reproductive organs of the snail.