Yuan H, Tang F, Pang S F
Department of Physiology, University of Hong Kong.
J Pineal Res. 1990;9(3):179-91. doi: 10.1111/j.1600-079x.1990.tb00707.x.
The [125I]-iodomelatonin binding sites in chicken brain membrane preparations were studied. The binding of [125I]-iodomelatonin to the membrane preparations of chicken brain was rapid, stable, saturable, and reversible. The order of pharmacological affinities of [125I]-iodomelatonin binding sites in the chicken brain membrane preparations was: melatonin greater than 6-chloromelatonin greater than N-acetylserotonin greater than 5-hydroxytryptamine greater than tryptamine greater than 5-methoxytryptophol, much greater than 1-acetylindole-3-carboxaldehyde, 5-hydroxyindole-3-acetic acid, L-tryptophan, 5-hydroxytryptophan, 3-acetylindole. Compounds known to act on the receptor of norepinephrine or acetylcholine were inactive as compared to melatonin. Among the various brain regions studied, melatonin binding had maximal level in the hypothalamus, intermediate levels in the mid-brain, ponsmedulla, and telencephalon, and minimum level in the cerebellum. Subcellular fraction studies indicated that 40% of the binding was located in the mitochondrial fraction, 27% in the nuclear, 26% in the microsomal, and 6% in the cytosol fraction. Scatchard analysis of the membrane preparations revealed a dissociation constant (Kd) of 199.6 +/- 17 pM and a total number of binding sites (Bmax) of 16.6 +/- 0.75 fmol/mg protein at midlight. Thus, our results showed the presence of specific melatonin binding sites in the chicken brain membrane preparations. Saturation studies demonstrated that [125I]-iodomelatonin binding capacity in chicken brain membrane preparations were 40% greater at midlight (16.6 +/- 0.75 fmol/mg protein) than at middark (10.6 +/- 0.56 fmol/mg protein), with no significant variation in their binding affinities.
研究了鸡脑膜制剂中的[125I] - 碘褪黑素结合位点。[125I] - 碘褪黑素与鸡脑膜制剂的结合迅速、稳定、可饱和且可逆。鸡脑膜制剂中[125I] - 碘褪黑素结合位点的药理亲和力顺序为：褪黑素＞6 - 氯褪黑素＞N - 乙酰血清素＞5 - 羟色胺＞色胺＞5 - 甲氧基色醇，远大于1 - 乙酰吲哚 - 3 - 甲醛、5 - 羟基吲哚 - 3 - 乙酸、L - 色氨酸、5 - 羟色氨酸、3 - 乙酰吲哚。与褪黑素相比，已知作用于去甲肾上腺素或乙酰胆碱受体的化合物无活性。在所研究的各个脑区中，褪黑素结合在下丘脑的水平最高，在中脑、脑桥延髓和端脑的水平居中，在小脑的水平最低。亚细胞组分研究表明，40%的结合位于线粒体组分，27%位于细胞核，26%位于微粒体，6%位于胞质溶胶组分。对膜制剂的Scatchard分析显示，在中等光照条件下，解离常数（Kd）为199.6±17 pM，结合位点总数（Bmax）为16.6±0.75 fmol/mg蛋白质。因此，我们的结果表明鸡脑膜制剂中存在特异性褪黑素结合位点。饱和研究表明，鸡脑膜制剂中[125I] - 碘褪黑素的结合能力在中等光照（16.6±0.75 fmol/mg蛋白质）时比在黑暗中期（10.6±0.56 fmol/mg蛋白质）高40%，其结合亲和力无显著差异。
