Kobayashi T, Shinnoh N, Goto I, Kuroiwa Y
J Biol Chem. 1985 Dec 5;260(28):14982-7.
Two genetically distinct acid beta-galactosidases are apparently involved in the hydrolysis of galactosylceramide in fibroblasts. These beta-galactosidases were activated by different bile salts. The classical galactosylceramidase (galactosylceramidase I, EC 3.2.1.46) was activated by sodium taurocholate, while the other galactosylceramidase (galactosylceramidase II) was activated by sodium cholate. The former was genetically lacking in globoid cell leukodystrophy (GLD) and the latter in GM1 gangliosidosis. Galactosylceramidase II cross-reacted with antibody raised against purified GM1 ganglioside beta-galactosidase (EC 3.2.1.23) from the human placenta. The purified beta-galactosidase had galactosylceramidase II activity, which was competitively inhibited by GM1 ganglioside. Thus, galactosylceramidase II seems to be identical to GM1 ganglioside beta-galactosidase and lactosylceramidase II. Galactosylceramidase II had a very low affinity for galactosylsphingosine. In the galactosylceramide-loading tests using fibroblasts from patients with GLD and GM1 gangliosidosis, both cell lines hydrolyzed the incorporated galactosylceramide, with lower rates than control fibroblasts but higher than the fibroblasts from patients with I-cell disease, in which both galactosylceramidase I and II were deficient. These results indicate that galactosylceramide is hydrolyzed by two genetically distinct beta-galactosidases and explain well that galactosylsphingosine but not galactosylceramide accumulates in the brain of patients with GLD.
两种基因不同的酸性β-半乳糖苷酶显然参与了成纤维细胞中半乳糖基神经酰胺的水解。这些β-半乳糖苷酶被不同的胆汁盐激活。经典的半乳糖基神经酰胺酶（半乳糖基神经酰胺酶I，EC 3.2.1.46）被牛磺胆酸钠激活，而另一种半乳糖基神经酰胺酶（半乳糖基神经酰胺酶II）被胆酸钠激活。前者在球状细胞脑白质营养不良（GLD）中基因缺失，后者在GM1神经节苷脂病中基因缺失。半乳糖基神经酰胺酶II与针对从人胎盘中纯化的GM1神经节苷脂β-半乳糖苷酶（EC 3.2.1.23）产生的抗体发生交叉反应。纯化的β-半乳糖苷酶具有半乳糖基神经酰胺酶II活性，该活性被GM1神经节苷脂竞争性抑制。因此，半乳糖基神经酰胺酶II似乎与GM1神经节苷脂β-半乳糖苷酶和乳糖基神经酰胺酶II相同。半乳糖基神经酰胺酶II对半乳糖基鞘氨醇的亲和力非常低。在使用GLD和GM1神经节苷脂病患者的成纤维细胞进行的半乳糖基神经酰胺负载试验中，两种细胞系都能水解掺入的半乳糖基神经酰胺，其速率低于对照成纤维细胞，但高于I型细胞病患者的成纤维细胞，后者的半乳糖基神经酰胺酶I和II均缺乏。这些结果表明，半乳糖基神经酰胺被两种基因不同的β-半乳糖苷酶水解，很好地解释了为什么在GLD患者的大脑中积累的是半乳糖基鞘氨醇而不是半乳糖基神经酰胺。
