Devreotes P N, Fambrough D M
J Cell Biol. 1975 May;65(2):335-58. doi: 10.1083/jcb.65.2.335.
[125I mono-iodo-alpha-bungarotoxin is used as a specific marker in a description of acetylcholine receptor metabolism. It is concluded that acetylcholine receptors in the surface membranes of chick and rat myotubes developing in cell cultures have a half-life of 22-24 h. Alpha-bungarotoxin (bound to a receptor which is removed from the membrane) is degraded to monoiodotyrosine which appears in the medium. Several observations are consistent with a model in which receptors or alpha-bungarotoxin-receptor complexes are internalized and then degraded: (a) the rate of appearance of iodotyrosine does not reach its maximal rate until 90 min after alpha-bungarotoxin is bound to the surface receptors; (b) 2,4-dinitrophenol, reduced temperature, and cell disruption all inhibit the degradation process. The degradation of surface receptors is not coupled to the process by which receptors are incorporated into the membrane. Evidence suggest that receptors are incorporated into the surface membrane from a presynthesized set of receptors containing about 10% as many alpha-bungarotoxin binding sites as does the surface. Additionally, a third set of acetylcholine receptors is described containing about 30% as amny binding sites as does the surface. These "hidden" recptors are not precursors yet are not readily accessible for binding of extracellular alpha-bungarotoxin. These findings are discussed in relation to both plasma membrane biosynthesis and control of chemosensitivity in developing and denervated skeletal muscle.
125I单碘α-银环蛇毒素被用作描述乙酰胆碱受体代谢的特异性标记物。得出的结论是，在细胞培养中发育的鸡和大鼠肌管表面膜中的乙酰胆碱受体半衰期为22 - 24小时。α-银环蛇毒素（与从膜上移除的受体结合）降解为单碘酪氨酸，后者出现在培养基中。一些观察结果与以下模型一致：受体或α-银环蛇毒素-受体复合物被内化然后降解：（a）直到α-银环蛇毒素与表面受体结合90分钟后，碘酪氨酸的出现速率才达到最大值；（b）2,4-二硝基苯酚、降低温度和细胞破碎都抑制降解过程。表面受体的降解与受体整合到膜中的过程无关。有证据表明，受体是从一组预先合成的受体整合到表面膜中的，该组受体含有的α-银环蛇毒素结合位点约为表面受体的10%。此外，还描述了第三组乙酰胆碱受体，其结合位点约为表面受体的30%。这些“隐藏”的受体不是前体，但细胞外α-银环蛇毒素不易与之结合。结合质膜生物合成以及发育中和去神经支配的骨骼肌中的化学敏感性控制对这些发现进行了讨论。
