Opioid Peptides from Milk Proteins

Abstract

Fragment peptides of milk proteins containing Tyr-X-Phe or Tyr-X₁-X₂-Phe were synthesized and their opioid activities were evaluated by the guinea pig ileum and radioreceptor assays. Among the peptides tested, the human β-casein(51 - 54) amide, Tyr-Pro-Phe-Val-NH2 (valmuceptin) was the most active, more than the bovine counterpart, morphiceptin. The human β-casein(41 - 44) amide, Tyr-Pro-Ser-Phe-NH2, and the α-lactalbumin (50-53) amide, Tyr-Gly-Leu-Phe-NH2, were also active in the guinea pig ileum assay. These were named β-casorphin and α-lactorphin, respectively. All of these peptides were not as active in the mouse and rabbit vas deferens assays.