title: Selective inhibition of 'motor endplate-specific' acetylcholinesterase by beta-endorphin and related peptides.
abstract: The effects of beta-endorphin (lipotropin 61-91) and related naturally-occurring peptides upon acetylcholinesterase activity in rat hind-limb muscles was investigated. beta-endorphin weakly inhibited the activity in a plasma membrane-enriched fraction. The inhibition by beta-endorphin of the membrane-associated acetylcholinesterase was less marked when the fractions were prepared from muscles which had been denervated 4-6 days previously. The membrane-associated acetylcholinesterase was solubilised from normal muscle preparations and separated by sucrose density gradient centrifugation into three major peaks (16S, 10S and 4S). beta-Endorphin inhibited the activity in the 16S peak but not that in the 10S and 4S peaks, whilst tensilon, a competitive inhibitor of acetylcholinesterase, inhibited the activity of all three peaks. beta-Endorphin inhibited the activity in the 16S peak but not that in the 10S and 4S peaks, whilst tensilon, a competitive inhibitor of acetylcholinesterase, inhibited the activity of all three peaks. beta-Endorphin inhibited the 16S activity in a concentration-dependent manner and its action was partly prevented if naloxone was added simultaneously. Purified natural porcine and bovine beta-endorphin were equipotent in terms of effective concentration range but the maximum inhibition was greater with the bovine peptide. beta-Lipotropin was approximately 4 times less potent than beta-endorphin, whilst C-fragment (lipotropin 61-87) was 100 times less potent. Prolonged treatment with collagenase did not reduce the catalytic activity of 16S acetylcholinesterase, but it was no longer susceptible to the inhibitory action of beta-endorphin. Kinetic studies indicated a complex type of inhibition by beta-endorphin (hyperbolic Lineweaver-Burke plot). Methionine enkephalin inhibited acetylcholinesterase in a weakly non-competitive manner and its action was not abolished if the enzyme was predigested with collagenase. beta-Endorphin produces a novel form of inhibition of acetylcholinesterase, acting only on the 16S (A12 or 'motor endplate-specific') form of the enzyme. The findings are discussed in the light of evidence that beta-endorphin-related immunoreactivity is expressed in motor nerve axons in the immature rat.
mesh_terms: D000818:Animals; D002384:Catalysis; D002800:Cholinesterase Inhibitors; D004491:Edrophonium / Q000494:pharmacology; D004723:Endorphins / Q000494:pharmacology*; D005260:Female; D003012:Microbial Collagenase; D009045:Motor Endplate / Q000201:enzymology*; D009121:Muscle Denervation; D009270:Naloxone / Q000494:pharmacology; D009469:Neuromuscular Junction / Q000201:enzymology*; D010455:Peptides / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D001615:beta-Endorphin
chemical_list: D002800:Cholinesterase Inhibitors; D004723:Endorphins; D010455:Peptides; D009270:Naloxone; D001615:beta-Endorphin; D004491:Edrophonium; D003012:Microbial Collagenase