[Met5]-Enkephalin, amide

[Met5]-Enkephalin, amide is an agonist for δ opioid receptors as well as putative ζ (zeta) opioid receptors.Met-enkephalin circulates in several forms, some of which may be derived from proteins other than proenkephalin A, and plasma levels of both free native, and peptidase-derivable Met-enkephalin are modulated physiologically.