Identification and primary structural analysis of peptide II, an end-product of precursor processing in cells R3-R14 of Aplysia

Abstract Peptide II, which is encoded on a gene for a precursor protein in abdominal ganglion neurons R 3 -R 14 , was purified from extracts of abdominal ganglia of Aplysia californica . Native peptide II comigrates with synthetic standards on HPLC under isocratic conditions. Amino acid sequence and composition analyses indicate that the sequence of peptide II is Glu-Ala-Glu-Glu-Pro-Ser-Phe-Met-Thr-Arg-Leu, as predicted from the precursor. The molluscan cardioexcitatory peptide Phe-Met-Arg-Phe-amide was also identified in abdominal ganglion extracts by similar means. The large amount of peptide II recovered (100 ng/ganglion), and its location on the precursor between two pairs of basic residues, strongly suggest that the precursor is processed into peptide II and at least two other peptides. Although cells R 3 -R 14 have been postulated to play a role in cardiovascular control, peptide II was without effect at ≤10 −4 M concentrations on identified abdominal ganglion neurons, the gastroesophageal artery or the heart. The physiological role of peptide II therefore remains to be elucidated.