Endomorphin

Endomorphins are two endogenous opioid peptides. Endomorphin-1 (Tyr-Pro-Trp-Phe-NH2) and endomorphin-2 (Tyr-Pro-Phe-Phe-NH2) are tetrapeptides with the highest known affinity and specificity for the μ opioid receptor. It is assumed that endomorphins are the cleavage products of a larger precursor, but this polypeptide or protein has not yet been identified.