Isolation and characterization of opioid antagonist peptides derived from human lactoferrin.
Peptides with affinity for opioid receptors were found in an artificially methyl-esterified peptic digest of human lactoferrin. Three active peptides were purified by two steps of reverse-phase high-performance liquid chromatography. Their structures were Tyr-Leu-Gly-Ser-Gly-Tyr-OCH3, Arg-Tyr-Tyr-Gly-Tyr-OCH2, and Lys-Tyr-Leu-Gly-Pro-Gln-Tyr-OCH3, which respectively correspond to the methyl esters of residues 318-323, 536-540, and 673-679 of human lactoferrin. The IC50 values of these peptides were 15, 10 and 23 microM, respectively, in a radioreceptor assay in the presence of 1 nM [3H]naloxone. In the myenteric plexus preparation of the longitudinal muscle of guinea pig ileum, the individual peptides had no opioid agonist activities, but they antagonized [Met5]enkephalin and morphiceptin when they were at a concentration of 10(-6)-10(-5) M, suggesting that these were the opioid antagonist peptides. These three opioid antagonist peptides were named lactoferroxin A, B and C, after casoxin, the opioid antagonist peptide derived from bovine kappa-casein. Concerning the antagonist activities of lactoferroxins for opioid receptor sub-types, lactoferroxin A showed preference for mu-receptors, while lactoferroxin B and C had somewhat higher degrees of preference for kappa-receptors than for mu-receptors. A study of the structure-activity relationship of the three lactoferroxins and their synthetic analogues showed that these opioid antagonist peptides derived from food protein could be expressed by the general formula XA-Tyr-XB-Tyr-OCH3. An amino acid in position XA may affect the specificity of the antagonist peptide for opioid receptor sub-types.
Department of Food Science and Technology, Faculty of Agriculture, Kyoto University, Japan.
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Tani
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Yoshikawa
D000595:Amino Acid Sequence; D006801:Humans; D007781:Lactoferrin / Q000302:isolation & purification* / Q000378:metabolism / Q000502:physiology; D008969:Molecular Sequence Data; D009292:Narcotic Antagonists / Q000302:isolation & purification*; D009842:Oligopeptides / Q000378:metabolism / Q000502:physiology; D010446:Peptide Fragments / Q000302:isolation & purification* / Q000378:metabolism / Q000502:physiology; D010455:Peptides / Q000302:isolation & purification*; D011957:Receptors, Opioid / Q000145:classification / Q000378:metabolism*; D013329:Structure-Activity Relationship
D009292:Narcotic Antagonists; D009842:Oligopeptides; D010446:Peptide Fragments; D010455:Peptides; D011957:Receptors, Opioid; C067917:lactoferroxin-A; C067918:lactoferroxin-B; C067919:lactoferroxin-C; D007781:Lactoferrin