Tauber R, Nuck R, Gerok W, Büchsel R, Köttgen E, Lohle W, Karasiewicz C, Reutter W
Institut für Klinische Chemie und Biochemie, Freie Universität Berlin, Germany.
Glycoconj J. 1992 Jun;9(3):132-40. doi: 10.1007/BF00780760.
The effect of vitamin A deficiency on N-linked oligosaccharides of membrane glycoproteins was studied in rat liver in order to evaluate the suggested role of retinol in protein N-glycosylation. First, oligosaccharides of newly synthesized glycoproteins from rough endoplasmic reticulum of vitamin A deficient liver were compared with that of pair-fed controls. Oligosaccharides were metabolically labelled with D-[2-3H]mannose, released from the glycoproteins with endoglycosidase H, purified by reversed phase HPLC and ion exchange chromatography, and were reduced with sodium borohydride. HPLC fractionation of the oligosaccharide alditols showed that the glycoproteins carried mainly four oligosaccharide species, Glc1Man9GlcNAc2, Man9GlcNAc2, Man8GlcNAc2 and Man7GlcNAc2, in identical relative amounts in the vitamin A deficient and the control tissue. In particular, no increase in the proportion of short chain oligosaccharides was noted in vitamin A deficient liver. Second, the number of N-linked oligosaccharides was estimated in dipeptidylpeptidase IV (DPP IV), a major glycoprotein constituent of the hepatic plasma membrane, comparing the newly synthesized glycoprotein from rough endoplasmic reticulum and the mature form of DPP IV from the plasma membrane. No evidence was obtained that retinol deficiency caused incomplete glycosylation of this membrane glycoprotein. From these data, the suggested role of retinol as a cofactor involved in the synthesis of N-linked oligosaccharides of glycoproteins must be questioned.
为了评估视黄醇在蛋白质 N-糖基化中所假定的作用，研究了维生素 A 缺乏对大鼠肝脏膜糖蛋白 N-连接寡糖的影响。首先，将维生素 A 缺乏肝脏的糙面内质网中新合成糖蛋白的寡糖与配对喂养对照的寡糖进行比较。寡糖用 D-[2-³H]甘露糖进行代谢标记，用内切糖苷酶 H 从糖蛋白中释放出来，通过反相高效液相色谱和离子交换色谱进行纯化，并用硼氢化钠还原。寡糖醇的高效液相色谱分级分离表明，维生素 A 缺乏组织和对照组织中的糖蛋白主要携带四种寡糖种类，即 Glc1Man9GlcNAc2、Man9GlcNAc2、Man8GlcNAc2 和 Man7GlcNAc2，其相对含量相同。特别是，在维生素 A 缺乏的肝脏中未观察到短链寡糖比例的增加。其次，通过比较糙面内质网中新合成的糖蛋白和质膜中成熟形式的二肽基肽酶 IV（DPP IV，肝细胞膜的主要糖蛋白成分），估计了 N-连接寡糖的数量。没有证据表明视黄醇缺乏会导致这种膜糖蛋白的糖基化不完全。根据这些数据，视黄醇作为参与糖蛋白 N-连接寡糖合成的辅助因子所假定的作用必须受到质疑。
