Brunngraber E G, Davis L G, Somawardhana C W
Neurochem Res. 1982 Oct;7(10):1243-56. doi: 10.1007/BF00965895.
Glycoproteins that contain phosphohexosyl groups were found to be present in the myelin- and synaptosomal-enriched fractions as well as in the microsomes of rat brain. The kinetics of flow of intraperitoneally injected [32P]phosphate suggests that the phosphate is enzymatically added in structures found in the microsomal fraction. The newly synthesized phosphoglycoproteins then appear in the soluble fraction of the synaptosomes and in the cytosol, prior to incorporation into the membranes of the synaptosomes and myelin. Phosphoglycopeptides recovered from the phosphoglycoprotein contain 3 Mannose units per N-acetylglucosamine residue; one of the mannose residues is phosphorylated. [13C]NMR studies indicate that the phosphoglycopeptides contain a chitobiose group and more than four sugar residues. Thus, the phosphomannoglycopeptides from rat brain contain an average of 2 N-acetylglucosamine, 6 mannose, and two phosphate moieties per oligosaccharide chain. Enzymatic treatment with alpha-mannosidase failed to remove the phosphomannose, although some mannose residues were released. Thus, the phosphorylated mannose is not removed by the glycosidase and terminal nonphosphorylated mannose residues are present in the oligosaccharide. The phosphate residues are removed by treatment with alkaline phosphatase.
含有磷酸己糖基的糖蛋白存在于大鼠脑富含髓磷脂和突触体的组分以及微粒体中。腹腔注射[32P]磷酸盐的流动动力学表明，磷酸盐是通过酶促作用添加到微粒体组分中的结构上的。新合成的磷酸糖蛋白随后出现在突触体的可溶性组分和细胞质中，然后才整合到突触体和髓磷脂的膜中。从磷酸糖蛋白中回收的磷酸糖肽每个N-乙酰葡糖胺残基含有3个甘露糖单元；其中一个甘露糖残基被磷酸化。[13C]核磁共振研究表明，磷酸糖肽含有一个壳二糖基团和超过四个糖残基。因此，大鼠脑的磷酸甘露糖肽每条寡糖链平均含有2个N-乙酰葡糖胺、6个甘露糖和两个磷酸基团。用α-甘露糖苷酶进行酶处理未能去除磷酸甘露糖，尽管释放了一些甘露糖残基。因此，磷酸化的甘露糖不会被糖苷酶去除，并且寡糖中存在末端非磷酸化的甘露糖残基。通过用碱性磷酸酶处理可以去除磷酸残基。
