van den Eijnden D H, Blanken W M, van Vliet A
Carbohydr Res. 1986 Aug 15;151:329-35. doi: 10.1016/s0008-6215(00)90352-5.
The "branch specificities" of the beta-D-galactosidases from Escherichia coli, jack bean, Aspergillus niger, and human liver were investigated with two branched oligosaccharide substrates, one which forms part of a complex-type biantennary N-linked glycan (compound 1) and a structure having blood group I activity (compound 2), respectively. Both substrates were available as radioactive compounds having a known distribution of 3H and 14C label in each of the terminal galactosyl groups, which allowed accurate estimation of the branch specificity of the enzymes from the ratio of 3H and 14C radioactivity in the galactose released by these hydrolases. It was found that the beta-D-galactosidase from E. coli preferentially released the galactosyl group at the 1----3 branch of compound 1 and that the 1----6 branch of compound 2. By contrast, the other beta-D-galactosidases investigated showed little or no branch specificity. These results suggest that the branch specificity of the beta-D-galactosidase from E. coli has to be explained from a specific recognition of certain parts of the aglycon of the substrates by this enzyme rather than from a better accessibility of the galactose at one particular branch.
利用两种分支寡糖底物研究了来自大肠杆菌、刀豆、黑曲霉和人肝脏的β-D-半乳糖苷酶的“分支特异性”，一种底物构成复合型双天线N-连接聚糖的一部分（化合物1），另一种底物具有血型I活性结构（化合物2）。两种底物均为放射性化合物，每个末端半乳糖基中3H和14C标记的分布已知，这使得可以根据这些水解酶释放的半乳糖中3H和14C放射性的比例准确估计酶的分支特异性。结果发现，大肠杆菌的β-D-半乳糖苷酶优先释放化合物1的1----3分支处的半乳糖基和化合物2的1----6分支处的半乳糖基。相比之下，所研究的其他β-D-半乳糖苷酶几乎没有或没有分支特异性。这些结果表明，大肠杆菌的β-D-半乳糖苷酶的分支特异性必须通过该酶对底物糖苷配基某些部分的特异性识别来解释，而不是通过特定分支处半乳糖更好的可及性来解释。
