In almost all studies involving localization or quantitation of regulatory peptides, an essential prerequisite is the generation of specific antisera in rabbits. Despite this almost universal practice, the primary structures of some established regulatory peptides, such as pancreatic polypeptide (PP), of the rabbit, remain unknown. 2. Here we report the full primary structure of PP isolated from extracts of rabbit pancreas. 3. PP immunoreactivity was purified using an antiserum (PP 221) generated to the highly-conserved C-terminal hexapeptide amide of mammalian PP. A single molecular form of rabbit PP was consistently resolved during sequential chromatographic fractionations. 4. Automated Edman degradation established the full primary structure as: APPEPVYPGDDATPEQMAEYVADLRRYINMLTRPRY. The molecular mass derived from this sequence (4196.7 Da), was in full agreement with that determined by mass spectroscopy (4196 Da). The peptide was deemed to be C-terminally amidated due to its full molar crossreactivity with the amide-requiring PP antiserum employed. 5. When compared with all other known mammalian PP sequences, rabbit PP displays three unique substituted sites, Pro at position 3, Glu at position 19 and Val at position 21.
