Clement-Jones V, Lowry P J, Rees L H, Besser G M
Nature. 1980 Jan 17;283(5744):295-7. doi: 10.1038/283295a0.
The physiological roles of Met-enkephalin and Leu-enkephalin are still unknown. They may act as neurotransmitters in the central and peripheral nervous systems. Met-enkephalin has been detected in several species in a variety of tissues including brain, spinal cord and gut using bioassays, opiate receptor assays and radioimmunoassays (RIA). It has also been detected in human gut immunocytochemically and in human brain and cerebrospinal fluid by opiate receptor assay and RIA. However, all reported assays show some degree of cross-reaction with Leu-enkephalin and unequivocal differentiation between the two enkephalins and the larger endorphins has not always been possible. Thus the existence of Met-enkephalin in human tissues and fluids remains in doubt. Using a highly specific RIA, we have now obtained evidence that Met-enkephalin-like material circulates in the plasma of normal subjects and may be secreted by the adrenal gland. Chromatographically the material exists in plasma mainly as the intact pentapeptide and not as the biologically inactive degradation product Gly-Gly-Phe-Met as would be expected from metabolic studies.
甲硫氨酸脑啡肽和亮氨酸脑啡肽的生理作用仍然未知。它们可能在中枢神经系统和外周神经系统中充当神经递质。利用生物测定法、阿片受体测定法和放射免疫测定法（RIA），在包括脑、脊髓和肠道在内的多种组织中已在多个物种中检测到甲硫氨酸脑啡肽。通过阿片受体测定法和RIA，还在人体肠道中通过免疫细胞化学方法以及在人脑和脑脊液中检测到了甲硫氨酸脑啡肽。然而，所有报道的测定法都显示出与亮氨酸脑啡肽有一定程度的交叉反应，并且并非总能明确区分这两种脑啡肽与更大的内啡肽。因此，人体组织和体液中甲硫氨酸脑啡肽的存在仍存疑问。我们现在使用一种高度特异性的放射免疫测定法获得了证据，表明甲硫氨酸脑啡肽样物质在正常受试者的血浆中循环，并且可能由肾上腺分泌。从色谱分析来看，该物质在血浆中主要以完整的五肽形式存在，而不是如代谢研究预期的那样以无生物活性的降解产物甘氨酰 - 甘氨酰 - 苯丙氨酸 - 甲硫氨酸形式存在。
