A highly potent 3200-dalton adrenal opioid peptide that contains both a [Met]- and [Leu]enkephalin sequence.

A 3200-dalton adrenal enkephalin-containing peptide, designated peptide E, that exhibits high opiate activity in the guinea pig ileum longitudinal muscle preparation was purified, and its structure was determined. It contains an amino-terminal [Met]enkephalin sequence and a [Leu]enkephalin sequence at the carboxyl terminus. Sequence analysis revealed that peptide E arises from a previously characterized 4900-dalton adrenal enkephalin-containing peptide. Peptide E was shown to be 30 times more potent than [Met]enkephalin in the guinea pig ileum assay, which suggests that the adrenal enkephalin-containing peptide may perform a unique biological function in vivo.