Detection of Met-enkephalin and Leu-enkephalin in the brain of the hagfish, Eptatretus stouti, and the lamprey, Petromyzon marinus.

Acid extracts of the brain of the pacific hagfish, Eptatretus stouti, and the marine lamprey, Petromyzon marinus, were each fractionated by gel filtration chromatography and aliquots of column fractions were screened with radioimmunoassays (RIAs) specific for pro-dynorphin-related end products and for pro-enkephalin-related end products. Only pro-enkephalin-related immunoreactive forms were detected. The enkephalin-sized immunoreactive material, isolated for each species, was separately fractionated by reverse-phase high-performance liquid chromatography (HPLC). Aliquots of column fractions were screened with RIAs specific for Met-enkephalin, Leu-enkephalin, Met-enkephalin-Arg-Phe, and Met-enkephalin-Arg-Gly-Leu. In the hagfish brain, immunoreactive forms with the same retention times as synthetic Met-enkephalin and Leu-enkephalin were detected in a ratio of approximately 2:1. In addition, an immunoreactive form was detected with the Met-enkephalin-Arg-Phe-specific RIA. This form had the same chromatographic properties as synthetic Met-enkephalin-Arg-Phe. Analyses with the Met-enkephalin-Arg-Gly-Leu RIA were negative. HPLC analysis of the lamprey enkephalin-related material revealed the presence of authentic Met-enkaphalin and Leu-enkephalin in a molar ratio of 3:1. C-terminally extended forms of Met-enkaphalin were not detected in the lamprey extracts. Collectively these observations indicate that pro-enkephalin-related opioid peptides are present in the brain of cyclostomes.