PeptidesReceptors, Opioid, muReceptors, OpioidAnalgesics, OpioidReceptors, Opioid, deltaReceptors, Opioid, kappaOpioid PeptidesPeptide FragmentsNarcotic AntagonistsPeptide LibraryNaloxoneOpioid-Related DisordersAntimicrobial Cationic PeptidesNaltrexoneEnkephalinsPeptides, CyclicOligopeptidesEnkephalin, Ala(2)-MePhe(4)-Gly(5)-EndorphinsMorphineNarcoticsPeptide MappingDynorphinsEnkephalin, D-Penicillamine (2,5)-Amino Acid SequenceEnkephalin, LeucineBuprenorphineEnkephalin, Leucine-2-AlanineNatriuretic Peptide, Brainbeta-EndorphinVasoactive Intestinal PeptideCalcitonin Gene-Related PeptidePainProtein BindingMolecular Sequence DataDiprenorphineCell-Penetrating PeptidesAnalgesicsPeptide BiosynthesisBenzeneacetamidesPeptide YYBinding SitesProtein PrecursorsModels, MolecularPeptide Nucleic AcidsDose-Response Relationship, DrugDrug ToleranceMorphinansNatriuretic Peptide, C-TypeStructure-Activity RelationshipProtein ConformationFentanylNatriuretic PeptidesPain MeasurementProtein Structure, SecondaryMethadoneKineticsGastrin-Releasing PeptideChromatography, High Pressure LiquidReceptors, Formyl PeptideHydromorphonePeptide PHIPeptide SynthasesBase SequencePeptide HydrolasesReceptors, PeptideCell LineAtrial Natriuretic FactorEpitopesBenzomorphansMass SpectrometryPyrrolidinesRats, Sprague-DawleyBinding, CompetitiveAnalgesiaSequence Homology, Amino AcidSubstance Withdrawal SyndromeTrypsinAmino AcidsRecombinant ProteinsProtein Structure, TertiaryOpiate Substitution TreatmentIntracellular Signaling Peptides and ProteinsCloning, MolecularPeptide HormonesCells, CulturedHeroinSubstrate SpecificityAmphibian ProteinsChronic PainMolecular MimicryCattlePrescription Drug MisuseLevorphanolCell MembraneMagnetic Resonance SpectroscopyMorphine DependenceSpectrometry, Mass, Matrix-Assisted Laser Desorption-IonizationTime FactorsMolecular Weight