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 (YGGFLRRQFKVVT). 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<sup>1</sup> and Phe<sup>4</sup> residues are critical for both opioid receptor affinity and ú-opioid receptor agonist potency, Arg<sup>6</sup> and Arg<sup>7</sup> promote ú-opioid affinity and Lys<sup>10</sup> contributes to the opioid receptor affinity.
Cannabinoid CP55,940 and â³<sup>9</sup>-tetrahydrocannabinol (â³<sup>9</sup>-THC) can induce the release of dynorphin B, which in return acts as an agonist of ú-opioid receptors, resulting in the production of antinociception. Similarly, Tyr-D-Arg-Phe-Sar (TAPS) is capable of promoting a release of dynorphin B through the simulation of ü<sub>1</sub>-opioid receptors, causing a production of antinociception. The antinociceptive effect produced by dynorphin B allows for spinal analgesia.