Basu M, Basu S S, Li Z, Tang H, Basu S
Department of Chemistry and Biochemistry, University of Notre Dame, IN 46556.
Indian J Biochem Biophys. 1993 Dec;30(6):324-32.
This report concerns the stepwise biosynthesis in vitro of Sialyl Lewis X, (SA-Le(x)), a carcinoembryonic antigen, in human colon carcinoma KM12 cells exhibiting different metastatic behaviors. The significance of SA-Le(x) has become even more apparent since the detection of its terminal epitope NeuAc(alpha 2-3)Gal beta 1-4(Fuc alpha 1-3)GlcNAc-, as the binding ligand of the selectin family member ELAM-1. The activity level of galactosyltransferase GalT-4 which catalyzes the formation of core nLcOse4Cer (Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc-Cer) is very high in all the metastatic lines tested with highly metastatic lines (KM12-SM) exhibiting the highest activity. The same activity pattern for galactosyltransferase is also observed when tested with iLcOse5Cer (GlcNAc beta 1-3nLcOse4Cer), the precursor for polylactosamine glycolipid. Sialyltransferase SAT-3 which catalyzes the formation of LM1 (NeuAc alpha 2-3nLcOse4Cer), the precursor for SA-Le(x), is also present in all the metastatic cell lines although the activity levels are much lower compared to galactosyltransferase. The fucosyltransferase FucT-3, which catalyzes the formation of R'-Gal-Fuc(alpha 1-3)GlcNAc-R linkage, is active with both nonsialylated substrate, nLcOse4Cer, and sialylated substrate, LM1 (NeuAc alpha 2-3nLcOse4Cer) with the formation of either Le(x) (Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3Gal beta 1-4Glc-Cer) or SA-Le(x) (NeuAc alpha 2-3nLcOse4Cer). However, the sialylated substrate LM1 is preferred to enzymatic activity since it exhibited lower Km (46 microM) than that of nLcOse4Cer (67 microM).(ABSTRACT TRUNCATED AT 250 WORDS)
本报告涉及在具有不同转移行为的人结肠癌KM12细胞中，癌胚抗原唾液酸化路易斯X（SA-Le(x)）的体外逐步生物合成。自从检测到其末端表位NeuAc(α2-3)Galβ1-4(Fucα1-3)GlcNAc-作为选择素家族成员ELAM-1的结合配体以来，SA-Le(x)的重要性变得更加明显。催化核心nLcOse4Cer（Galβ1-4GlcNAcβ1-3Galβ1-4Glc-Cer）形成的半乳糖基转移酶GalT-4的活性水平，在所有测试的转移细胞系中都非常高，其中高转移细胞系（KM12-SM）的活性最高。当用多乳糖胺糖脂的前体iLcOse5Cer（GlcNAcβ1-3nLcOse4Cer）进行测试时，也观察到半乳糖基转移酶具有相同的活性模式。催化SA-Le(x)的前体LM1（NeuAcα2-3nLcOse4Cer）形成的唾液酸转移酶SAT-3，也存在于所有转移细胞系中，尽管其活性水平与半乳糖基转移酶相比要低得多。催化R'-Gal-Fuc(α1-3)GlcNAc-R连接形成的岩藻糖基转移酶FucT-3，对非唾液酸化底物nLcOse4Cer和唾液酸化底物LM1（NeuAcα2-3nLcOse4Cer）都有活性，可形成Le(x)（Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc-Cer）或SA-Le(x)（NeuAcα2-3nLcOse4Cer）。然而，唾液酸化底物LM1对酶活性更具偏好性，因为它的Km（46 microM）低于nLcOse4Cer（67 microM）。（摘要截短于250字）
