Kaizu T, Turco S J, Rush J S, Laine R A
J Biol Chem. 1982 Jul 25;257(14):8272-6.
Mouse GM979 erythroleukemic cells were found to synthesize the branched form of erythroglycan, a large polylactosamine structure known to be attached to band 3 and possibly to other proteins on human erythrocytes. Total protein-derived oligosaccharides from GM979 cells, labeled metabolically with [3H]glucosamine, [3H]mannose, or [3H]galactose, were prepared by hydrazinolysis after extracting the lipids. The 3H-labeled oligosaccharides were fractionated on Sephadex G-50 revealing 10-25% of each labeled product as a high molecular weight fraction (Mr = 10,000). Digestion of this [3H]glucosamine fraction with endo-beta-galactosidase from Escherichia freundii, specific for the repeating structure of Gal beta (1 leads to 4)GlcNAc beta (1 leads to 3), resulted in the following four products upon Bio-Gel P-2 Gel filtration: 1) a disaccharide with the structure GlcNAc beta (1 leads to 3)Gal, 2) a trisaccharide with the structure Gal beta (1 leads to 4)GlcNAc beta (1 leads to 3) beta Gal, 3) a tetrasaccharide with the sequence Fuc alpha (1 leads to 2)Gal beta (1 leads to 4)GlcNAc beta (1 leads to 3)Gal, and 4) a large complex fragment which contained mannose, glucosamine, galactose, and fucose (presumably the protein linkage region). Methylation linkage analysis of the large complex fraction shows mainly the presence of 4-substituted and terminal N-acetylglucosamine; 3,6-substituted, 6-substituted, 2-substituted, and 2,3-substituted galactose. The GM979 cell erythroglycan is only 30% susceptible to endo-beta-galactosidase degradation probably because of the branched galactose residues, whereas the linear form of erythroglycan from human K562 cells is 60% susceptible. The branched residues in GM979 cell saccharides indicate that this mouse cell line bears an arborized erythroglycan-like glycopeptide similar to those found on human adult erythrocytes, and thus may be a source for the enzyme which transfers an N-acetylglucosamine residue to a 3-linked galactose to form a 3,6-disubstituted galactose.
人们发现小鼠GM979红白血病细胞能合成支链形式的红细胞聚糖，这是一种已知与人类红细胞上的带3以及可能与其他蛋白质相连的大型聚乳糖胺结构。GM979细胞中源自总蛋白的寡糖，用[³H]葡糖胺、[³H]甘露糖或[³H]半乳糖进行代谢标记，在提取脂质后通过肼解制备。将³H标记的寡糖在Sephadex G - 50上进行分级分离，结果显示每种标记产物中有10 - 25%为高分子量部分（Mr = 10,000）。用弗氏埃希菌的内切β - 半乳糖苷酶消化该[³H]葡糖胺部分，该酶对Galβ(1→4)GlcNAcβ(1→3)的重复结构具有特异性，经Bio - Gel P - 2凝胶过滤后产生以下四种产物：1）结构为GlcNAcβ(1→3)Gal的二糖；2）结构为Galβ(1→4)GlcNAcβ(1→3)βGal的三糖；3）序列为Fucα(1→2)Galβ(1→4)GlcNAcβ(1→3)Gal的四糖；4）一个包含甘露糖、葡糖胺、半乳糖和岩藻糖的大复合片段（可能是蛋白质连接区）。对大复合部分进行甲基化连接分析表明主要存在4 - 取代和末端N - 乙酰葡糖胺；3,6 - 取代、6 - 取代、2 - 取代和2,3 - 取代的半乳糖。GM979细胞的红细胞聚糖仅30%易受内切β - 半乳糖苷酶降解，可能是因为存在支链半乳糖残基，而来自人类K562细胞的线性红细胞聚糖有60%易受降解。GM979细胞糖类中的支链残基表明该小鼠细胞系带有一种与人类成年红细胞上发现的类似的树状红细胞聚糖样糖肽，因此可能是将N - 乙酰葡糖胺残基转移至3 - 连接的半乳糖以形成3,6 - 二取代半乳糖的酶的来源。
