title: Interaction of beta-endorphin and other opioid peptides with calmodulin.
abstract: A highly purified preparation of calmodulin activated a calmodulin-deficient phosphodiesterase by more than 10-fold. This activation of phosphodiesterase by calmodulin was completely inhibited by two opioid peptides, beta-endorphin and dynorphin, at concentrations that had no appreciable effect on the basal phosphodiesterase activity. By contrast, similar concentrations of other structurally related peptides, including alpha-endorphin, (des-Tyr1)-gamma-endorphin, Leu-enkephalin, and Met-enkephalin, failed to block calmodulin's activation of phosphodiesterase. The inhibition by beta-endorphin of calmodulin's action was not reversed by calcium or by the opiate antagonist naloxone but was overcome by increasing the concentration of calmodulin. Equilibrium dialysis studies showed that 125I-labeled beta-endorphin bound directly to calmodulin in a saturable, calcium-dependent manner with a dissociation constant of approximately 4.6 microM. There was substantially less binding of beta-endorphin to troponin-C and little or no calcium-dependent binding of beta-endorphin to bovine serum albumin, lactalbumin, or histone. This interaction of beta-endorphin with calmodulin was similar in several respects to the interaction of certain antipsychotic drugs to calmodulin and may explain certain of the peptide's biochemical effects.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001711:Biotransformation / Q000187:drug effects; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002417:Cattle; D002746:Chlorpromazine / Q000494:pharmacology; D004723:Endorphins / Q000494:pharmacology*; D004744:Enkephalin, Methionine / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D066298:In Vitro Techniques; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D001615:beta-Endorphin
chemical_list: D002135:Calcium-Binding Proteins; D002147:Calmodulin; D004723:Endorphins; D004744:Enkephalin, Methionine; D001615:beta-Endorphin; D010727:Phosphoric Diester Hydrolases; D002746:Chlorpromazine