Figlewicz D A, Quarles R H, Johnson D, Barbarash G R, Sternberger N H
J Neurochem. 1981 Sep;37(3):749-58. doi: 10.1111/j.1471-4159.1982.tb12551.x.
Recent immunocytochemical studies indicated that the myelin-associated glycoprotein (MAG) is localized in the periaxonal region of central nervous system (CNS) and peripheral nervous system (PNS) myelin sheaths but previous biochemical studies had not demonstrated the presence of MAG in peripheral nerve. The glycoproteins in rat sciatic nerves were heavily labeled by injection of [3H]fucose in order to re-examine whether MAG could be detected chemically in peripheral nerve. Myelin and a myelin-related fraction, W1, were isolated from the nerves. Labeled glycoproteins in the PNS fractions were extracted by the lithium diiodosalicylate (LIS)-phenol procedure, and the extracts were treated with antiserum prepared to CNS MAG in a double antibody precipitation. This resulted in the immune precipitation of a single [3H]fucose-labeled glycoprotein with electrophoretic mobility very similar to that of [14C]fucose-labeled MAG from rat brain. A sensitive peptide mapping procedure involving iodination with Bolton-Hunter reagent and autoradiography was used to compare the peptide maps generated by limited proteolysis from this PNS component and CNS MAG. The peptide maps produced by three distinct proteases were virtually identical for the two glycoproteins, showing that the PNS glycoprotein is MAG. The MAG in the PNS myelin and W1 fractions was also demonstrated by Coomassie blue and periodic acid-Schiff staining of gels on which the whole LIS-phenol extracts were electrophoresed, and densitometric scanning of the gels indicated that both fractions contained substantially less MAG than purified rat brain myelin. The presence of MAG in the periaxonal region of both peripheral and central myelin sheaths is consistent with a similar involvement of this glycoprotein in axon-sheath cell interactions in the PNS and CNS.
最近的免疫细胞化学研究表明，髓鞘相关糖蛋白（MAG）定位于中枢神经系统（CNS）和周围神经系统（PNS）髓鞘的轴突周围区域，但先前的生化研究尚未证实在周围神经中存在MAG。为了重新检查是否能从化学角度在周围神经中检测到MAG，通过注射[3H]岩藻糖对大鼠坐骨神经中的糖蛋白进行了大量标记。从神经中分离出髓鞘和一种与髓鞘相关的组分W1。采用二碘水杨酸锂（LIS）-苯酚法提取PNS组分中的标记糖蛋白，提取物用针对CNS MAG制备的抗血清进行双抗体沉淀处理。这导致一种单一的[3H]岩藻糖标记糖蛋白发生免疫沉淀，其电泳迁移率与大鼠脑[14C]岩藻糖标记的MAG非常相似。采用一种涉及用博尔顿-亨特试剂碘化和放射自显影的灵敏肽图分析方法，比较了该PNS组分和CNS MAG经有限蛋白酶水解产生的肽图。三种不同蛋白酶产生的肽图对于这两种糖蛋白几乎完全相同，表明PNS糖蛋白就是MAG。通过对经LIS-苯酚提取物进行电泳的凝胶进行考马斯亮蓝染色和高碘酸-希夫染色，也证实了PNS髓鞘和W1组分中存在MAG，凝胶的光密度扫描表明，这两个组分中的MAG含量均明显低于纯化的大鼠脑髓鞘。周围和中枢髓鞘轴突周围区域均存在MAG，这与该糖蛋白在PNS和CNS中轴突-髓鞘细胞相互作用中的类似作用是一致的。
