Isolation and structure of pro-methionine-enkephalin: Potential enkephalin precursor from porcine hypothalamus

A hexapeptide that we have named pro-methionine-enkephalin has been isolated from acid extracts of porcine hypothalami and found to have the amino acid sequence H-Tyr-Gly-Gly-Phe-Met(O)-Arg-OH. This peptide is not a fragment of either porcine beta-lipotropin or beta-endorphin, which suggests that it could be a precursor of [Met]enkephalin in the brain by a pathway differing from the one usually postulated. The existence of still larger precursors of [Met]enkephalin, perhaps related to the recently reported alpha-neo-endorphin, is strongly implied by these studies. Synthetic H-Tyr-Gly-Gly-Phe-Met-Arg-OH exhibited low, but significant, opiate activity in vitro.