Murphy R B, Pincus M R, Beinfeld M, Dykes D C, Chen J M, Schneider L H, Gibbs J, Smith G P
New York Hospital-Cornell University Medical Center, Department of Psychiatry, E. W. Bourne Laboratory, White Plains 10605.
J Protein Chem. 1992 Dec;11(6):723-9. doi: 10.1007/BF01024973.
Prior calculations based on ECEPP (Empirical Conformational Energies for Peptides Program) of the low energy minima for cholecystokinin (CCK) and Met-enkephalin have demonstrated that significant structural features of these two peptides are identical. This result suggested the possibility that Met-enkephalin, as well as other enkephalin analogues of similar structure, could associate with receptors for CCK. To test this theoretical result, we examined the ability of Met-enkephalin and its analogues to bind to peripheral CCK receptors in the rat gastrointestinal tract; in particular, we measured the ability of the opiate peptide to inhibit the effects of CCK in a physiological assay system which we have previously characterized: CCK-induced contraction of the isolated rat pyloric sphincter. We find that Met-enkephalin is an antagonist of the CCK-8-induced contraction, with a IC50 of 110 nM. Furthermore, antibodies against CCK were found to cross-react with Met-enkephalin and its analogues in a manner which suggests a distinct structure-activity relationship. These experimental results strongly support the theoretical results of conformational analysis showing structural similarity between enkephalin and CCK. They further suggest that enkephalins could modulate the response of CCK systems under physiological conditions.
先前基于ECEPP（肽的经验构象能量程序）对胆囊收缩素（CCK）和甲硫氨酸脑啡肽低能量最小值的计算表明，这两种肽的显著结构特征是相同的。这一结果提示了甲硫氨酸脑啡肽以及其他结构相似的脑啡肽类似物可能与CCK受体结合的可能性。为了验证这一理论结果，我们检测了甲硫氨酸脑啡肽及其类似物与大鼠胃肠道外周CCK受体结合的能力；具体而言，我们在一个我们之前已进行过特性描述的生理检测系统中，测量了阿片肽抑制CCK作用的能力：CCK诱导的离体大鼠幽门括约肌收缩。我们发现甲硫氨酸脑啡肽是CCK-8诱导收缩的拮抗剂，IC50为110 nM。此外，发现抗CCK抗体与甲硫氨酸脑啡肽及其类似物发生交叉反应，其方式表明存在独特的构效关系。这些实验结果有力地支持了构象分析的理论结果，显示了脑啡肽与CCK之间的结构相似性。它们还进一步提示，脑啡肽在生理条件下可能调节CCK系统的反应。
