Dynorphin peptides are members of the opioid peptide family and contain the canonical opioid sequence Tyr-Gly-Gly-Phe. These peptides are derived from prodynorphin and include dynorphin A, dynorphin B and alpha neo-endorphin. Of the opioid peptides, the dynorphins have the highest affinity for the kappa opioid receptor. They are found distributed throughout the nervous system and play a role in many physiological functions.