Haynes L W, Smith M E, Li C H
Mol Pharmacol. 1984 Jul;26(1):45-50.
The molecular forms of acetylcholinesterase in extracts of gastrocnemius muscle from four vertebrate species and in electric eel (Electrophorus) electric organ were separated and identified by low-salt precipitation and velocity sedimentation. The activity of the heavy insoluble (A12) form of human muscle acetylcholinesterase was inhibited by synthetic human beta-endorphin (500 mM). The homologous form in rat muscle extracts was poorly inhibited by human beta-endorphin at the same concentration, but was more effectively inhibited by camel beta-endorphin. The activities of heavy forms of pseudocholinesterase, present in small amounts in both species, were not reduced by beta-endorphin. Selective inhibition of homologous heavy forms of acetylcholinesterase activity by camel and human beta-endorphin was also seen in skeletal muscle extracts from frog and pigeon, but with decreased effectiveness. No inhibition was detectable in the heavy acetylcholinesterase form from extracts of electric organ tissue of the electric eel. The inhibition of heavy acetylcholinesterase activity in human muscle by human beta-endorphin was dependent on the presence of its NH2-terminal pentapeptide sequence. Maximal inhibitory potency depended on the presence of the entire amino acid sequence, since potency was considerably reduced in synthetic peptide analogues lacking either middle or COOH-terminal segments of beta-endorphin. The relative potency of beta-endorphin from various species as inhibitors of rat heavy acetylcholinesterase activity was also investigated. beta-Endorphin sequences most closely resembling that of the rat peptide (camel, equine) were most potent, whereas those with sequence differences of more than one amino-acid were less potent (turkey, human) or had no inhibitory activity (ostrich). The selective inhibition of heavy acetylcholinesterase by beta-endorphin thus exhibits species specificity, even among mammals, in which homologues of this molecular form of the enzyme are otherwise indistinguishable.
通过低盐沉淀和速度沉降法，分离并鉴定了四种脊椎动物腓肠肌提取物以及电鳗（电鳐属）电器官中的乙酰胆碱酯酶分子形式。合成的人β-内啡肽（500 mM）可抑制人肌肉乙酰胆碱酯酶重质不溶性（A12）形式的活性。相同浓度下，人β-内啡肽对大鼠肌肉提取物中的同源形式抑制作用较弱，但骆驼β-内啡肽对其抑制效果更佳。两种物种中少量存在的假性胆碱酯酶重质形式的活性并未因β-内啡肽而降低。在青蛙和鸽子的骨骼肌提取物中，也观察到骆驼和人β-内啡肽对乙酰胆碱酯酶同源重质形式活性的选择性抑制，但效果有所降低。在电鳗电器官组织提取物的重质乙酰胆碱酯酶形式中未检测到抑制作用。人β-内啡肽对人肌肉中重质乙酰胆碱酯酶活性的抑制作用取决于其NH2末端五肽序列的存在。最大抑制效力取决于整个氨基酸序列，因为在缺乏β-内啡肽中间或COOH末端片段的合成肽类似物中，效力会显著降低。还研究了来自不同物种的β-内啡肽作为大鼠重质乙酰胆碱酯酶活性抑制剂的相对效力。与大鼠肽序列最相似的β-内啡肽序列（骆驼、马）效力最强，而氨基酸序列差异超过一个的则效力较弱（火鸡、人）或无抑制活性（鸵鸟）。因此，β-内啡肽对重质乙酰胆碱酯酶的选择性抑制表现出物种特异性，即使在哺乳动物中也是如此，而该酶这种分子形式的同源物在其他方面难以区分。
