Strous G J, Van Kerkhof P, Willemsen R, Slot J W, Geuze H J
Eur J Cell Biol. 1985 Mar;36(2):256-62.
The effect of monensin on the metabolism and glycosylation of the trans-Golgi enzyme galactosyltransferase (GT) was studied in HeLa cells. The synthesis of GT was not affected by monensin; however, in the presence of the drug GT precursor molecules (Mr 54 000 and 47 000) were transported to the Golgi system at a slower rate than in control cells. the half-life of GT as an intrinsic membrane protein of the trans-Golgi system was prolonged in the presence of monensin. Mature GT (Mr 54 000) contained in addition to one N-linked oligosaccharide several O-linked oligosaccharides; the majority of them consisted of the disaccharide galactose-N-acetylgalactosamine containing one or two sialic acid residues. We conclude that GT resides at an intracellular location where significant sialylation occurs. The sialylation of O-linked oligosaccharides was not hampered by the presence of monensin. Two-dimensional gel electrophoresis combined with neuraminidase treatment revealed that GT consists of a number of species in a pI range between 4 and 7. Removal of sialic acid residues resulted in a less acidic pI range of GT but the charge heterogeneity persisted. Immunoelectron microscopy with antibodies against GT showed that monensin affects primarily the GT-containing cisternae.
在HeLa细胞中研究了莫能菌素对反式高尔基体酶半乳糖基转移酶（GT）代谢和糖基化的影响。莫能菌素不影响GT的合成；然而，在药物存在的情况下，GT前体分子（分子量54 000和47 000）转运至高尔基体系统的速率比对照细胞慢。在莫能菌素存在的情况下，GT作为反式高尔基体系统内在膜蛋白的半衰期延长。成熟的GT（分子量54 000）除了一个N-连接寡糖外，还含有几个O-连接寡糖；其中大多数由含有一个或两个唾液酸残基的半乳糖-N-乙酰半乳糖胺二糖组成。我们得出结论，GT位于细胞内发生显著唾液酸化的位置。莫能菌素的存在并未阻碍O-连接寡糖的唾液酸化。二维凝胶电泳结合神经氨酸酶处理表明，GT由多个等电点在4至7之间的物种组成。去除唾液酸残基导致GT的等电点范围酸性降低，但电荷异质性仍然存在。用抗GT抗体进行免疫电子显微镜检查表明，莫能菌素主要影响含有GT的潴泡。
