Opioid peptides produced by in-vitro proteolysis of bovine caseins

Abstract

Abstract The formation of opioid peptides by in-vitro proteolysis of bovine caseins was investigated. Bovein α s1 -, β- and κ-caseins were predigested with pepsin and subsequently treated with either trypsin or trypsin + chymotrypsin. For separation and identification of the peptides, HPLC chromatography, protein sequencing and amino acid analysis were used. Digestion of α s1 -casein with pepsin alone yielded Arg-Tyr-Leu-Gly-Tyr-Leu ( α s1 -CN f90–95). Proteolysis of β-casein with pepsin and trypsin produced fragment Val-Tyr-Pro-Phe-Pro-Gly-Pro-Ile-Pro-Asn (β-CN f59–68), which contains the opioid fragment Tyr-Pro-Phe-Pro-Gly-Pro-Ile (β-CN f60–66) of β-casein. Digestion of κ-casein with pepsin for 24 h yielded Ser-Arg-Tyr-Pro-Ser-Tyr ( (κ-CN f33–38) although a higher degree of hydrolysis was achieved by addition of trypsin and chymotrypsin.