Rivera-Sagredo A, Cañada F J, Nieto O, Jimenez-Barbero J, Martín-Lomas M
Instituto de Química Orgánica, Consejo Superior de Investigaciones Científicas, Madrid, Spain.
Eur J Biochem. 1992 Oct 1;209(1):415-22. doi: 10.1111/j.1432-1033.1992.tb17304.x.
Lactase-phlorizin hydrolase is a disaccharidase present in the small intestine of mammals. This enzyme has two active sites, one being responsible for the hydrolysis of lactose. Lactase activity is thought to be selective towards glycosides with a hydrophilic aglycon. In this work, we report a systematic study on the importance of each hydroxyl group in the substrate molecule for lactase activity. For this purpose, all of the monodeoxy derivatives of methyl beta-lactoside and other lactose analogues are studied as lactase substrates. With respect to the galactose moiety, it is shown here that HO-3' and HO-2' are necessary for hydrolysis of the substrates by lactase. Using these chemically modified substrates, it has been confirmed that lactase does not behave as a typical beta-galactosidase, since it does not show an absolute selectivity with respect to substitution and stereochemistry at C4' in the galactose moiety of the substrate. However, the glucose moiety, in particular the HO-6, appears to be important for substrate hydrolysis, although none of the hydroxyl groups seemed to be essential. In order to differentiate both activities of the enzyme, a new assay for the phlorizin-hydrolase activity has also been developed.
乳糖酶 - 根皮苷水解酶是一种存在于哺乳动物小肠中的双糖酶。这种酶有两个活性位点，其中一个负责乳糖的水解。乳糖酶活性被认为对具有亲水性糖苷配基的糖苷具有选择性。在这项工作中，我们报告了一项关于底物分子中每个羟基对乳糖酶活性重要性的系统研究。为此，研究了甲基β - 乳糖苷和其他乳糖类似物的所有单脱氧衍生物作为乳糖酶底物。关于半乳糖部分，这里表明HO - 3'和HO - 2'是乳糖酶水解底物所必需的。使用这些化学修饰的底物，已证实乳糖酶的行为不同于典型的β - 半乳糖苷酶，因为它对底物半乳糖部分C4'处的取代和立体化学没有绝对选择性。然而，葡萄糖部分，特别是HO - 6，似乎对底物水解很重要，尽管没有一个羟基似乎是必不可少的。为了区分该酶的两种活性，还开发了一种新的根皮苷水解酶活性测定方法。
