Purification and sequencing of neuropeptides from identified neurons in the marine mollusc, Tritonia.

Neuropeptides were characterized in two similar identified neurons termed pedal 5 and 6 (Pd5 and Pd6). Both neurons appear white, a characteristic of peptidergic neurons, and send peripheral axons down several nerves that innervate the foot and control locomotion. Gel electrophoresis of neurons incubated with labeled amino acids indicated that individually dissected Pd5 and Pd6 neurons synthesized peptide precursors of the same size and processed them in parallel. Using HPLC, several absorbance peaks that had retention times typical of peptides were identified that were specific to extracts of Pd5 and Pd6. Three peptides were purified from extracts of many pooled Pd5 and Pd6 neurons. The complete sequences of two 15-amino acid peptides were obtained and the sequence of a third 15-amino acid peptide was inferred from the partial sequence of an apparent processing intermediate. Each of the three peptides show sequence homology to Aplysia pedal peptide (Pep). HPLC of neurons incubated with labeled amino acids demonstrated that Pd5 and Pd6 each synthesized all three sequenced peptides.