O -sulphated Leu-enkephalin in brain

The enkephalins appear to share a common precursor which is distinct from pro-opiocortin1,2. The adrenal proenkephalins have molecular weights (Mrs) in the range 5,000–30,000 with the largest species containing six copies of Met-enkephalin to one of Leu-enkephalin3. The brain proenkephalins appear to differ in that the molecular weights are in the range 5,000–90,000 and digestion of the largest protein with trypsin and carboxypeptidase B generates approximately equal proportions of Met- and Leu-enkephalin4. During our studies of brain proenkephalin we noted the generation of enkephalin-immunoreactive species that were chromatographically distinct from Met- and Leu-enkephalin. Here we identify one of these species as O-sulphated Leu-enkephalin and suggest possible roles for sulphation in the metabolism of opioid peptides.