Dynorphin B, also known as rimorphin, is a form of dynorphin and an endogenous opioid peptide with the amino acid sequence Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Gln-Phe-Lys-Val-Val-Thr. Dynorphin B is generated as a proteolytic cleavage product of leumorphin, which in turn is a cleavage product of preproenkephalin B (prodynorphin).
Dynorphin B has an identical N-terminal sequence, but different C-terminal sequence to Dynorphin A. In an alanine scan of the non-glycine residues of dynorphin B, it was discovered that Tyr and Phe residues are critical for both opioid receptor affinity and κ-opioid receptor agonist potency, Arg and Arg promote κ-opioid affinity and Lys contributes to the opioid receptor affinity.