Zingales B, Carniol C, de Lederkremer R M, Colli W
Departamento de Bioquímica, Universidade de São Paulo, Brazil.
Mol Biochem Parasitol. 1987 Nov;26(1-2):135-44. doi: 10.1016/0166-6851(87)90137-x.
Labeled sialoglycolipids were purified from tissue culture-derived trypomastigotes incubated with [3H]fetuin. Thin layer chromatography of [3H]sialoglycolipids showed three components with the same migration as gangliosides extracted from parasites incubated with [3H]palmitic acid. Neuraminidase treatment or mild acid hydrolysis confirmed the presence of [3H]sialyl residues in sialoglycolipids synthesized after [3H]fetuin incubation. Labeling was not observed when parasites were incubated with free [3H]sialic acid (C7 derivative), suggesting that sialyl residues are directly transferred in vivo to gangliosides, by an enzymatic reaction possibly catalysed by a sialyl transferase (transglycosylase). Sonicated extracts of trypomastigotes incubated with [3H]fetuin catalysed the labeling of endogenous glycoconjugates as well as of bovine brain gangliosides. The transglycosylase activity was found associated with the particulate fraction and could be solubilized with Triton X-100. The specific activity of the sialic acid transglycosylase in epimastigotes is 17% of that found in trypomastigotes. Addition of an excess free sialic acid did not inhibit the reaction, suggesting that transfer does not occur via a pool of free sialic acid.
将标记的唾液酸糖脂从与[3H]胎球蛋白孵育的组织培养衍生的锥鞭毛体中纯化出来。[3H]唾液酸糖脂的薄层色谱显示有三个组分，其迁移率与从用[3H]棕榈酸孵育的寄生虫中提取的神经节苷脂相同。神经氨酸酶处理或温和的酸水解证实了在[3H]胎球蛋白孵育后合成的唾液酸糖脂中存在[3H]唾液酸残基。当寄生虫与游离的[3H]唾液酸（C7衍生物）孵育时未观察到标记，这表明唾液酸残基在体内通过可能由唾液酸转移酶（转糖基酶）催化的酶促反应直接转移到神经节苷脂上。用[3H]胎球蛋白孵育的锥鞭毛体的超声提取物催化内源性糖缀合物以及牛脑神经节苷脂的标记。发现转糖基酶活性与颗粒部分相关，并且可以用 Triton X-100 溶解。在无鞭毛体中唾液酸转糖基酶的比活性是在锥鞭毛体中发现的比活性的 17%。加入过量的游离唾液酸不会抑制该反应，这表明转移不是通过游离唾液酸池发生的。
