Low molecular weight proteins of Aplysia neurosecretory cells.

The proteins of identified cells from the Aplysia californica central nervous system were labeled with radioactive amino acids and fractionated on SDS acrylamide gels containing 6 M urea. Most of the large cells contain prominent, cell-specific protein products in the molecular weight range between 3 and 30 KD. The molecular weights of the largest specific prevalent protein products are in good agreement with the predicted molecular weights of precursors as determined from an analysis of cDNA clones homologous to mRNA's specifically expressed in several of these neurons. Biologically active peptides have been found in many of these cells. These data, and other indirect evidence suggests that the synthesis of a large amount of a particular protein in this molecular weight range is indicative of the synthesis of a neurosecretory product. We conclude that most, if not all, large neurons in the Aplysia central nervous system are peptidergic.