CAT PROENKEPHALIN-A DOES NOT CONTAIN THE OPIOID OCTAPEPTIDE

The sequence of a large cDNA fragment of proenkephalin-A from the cat adrenal medulla was obtained using reverse transcription followed by p olymerase chain reaction, and cloning. This cDNA encompasses the regio n normally containing ail the opioid peptides, except the C-terminal h eptapeptide. As with other species, cat proenkephalin-A contains four conserved copies of (Met(5))-enkephalin, and one of (Leu(5))-enkephali n, flanked by processing sites of paired basic amino acids. However, s ignificant differences were found in the nucleotide and deduced amino acid sequences in the region of the octapeptide. In particular, the es sential tyrosyl residue is substituted by a histidyl residue, making i t unlikely that the cat equivalent would have opioid activity. Further more, the peptide is not flanked by paired basic residues, suggesting it is not processed.