Leparoux S, Padrines M, Placier G, Colas B
Laboratoire de Biochimie, UPRES 2161, Centre de Recherche de Biologie et Physico-chimie Cellulaires, Faculté des Sciences et des Techniques, Nantes, France.
Biochim Biophys Acta. 1997 Oct 20;1336(3):522-32. doi: 10.1016/s0304-4165(97)00065-2.
An acid beta-galactosidase was isolated from the digestive juice of Achatina achatina and purified to homogeneity by anion exchange, gel-filtration and hydroxyapatite chromatographies. This enzyme is soluble, as are the cytosolic beta-galactosidases, functions at acid pH like the lysosomal enzymes but differs from the other soluble animal beta-galactosidases in that it is highly specific for the beta-D-galactosyl residue. In addition, it cleaves the beta1-4 linkage much faster than the beta1-3 and beta1-6 linkages. The enzyme is a monomeric glycoprotein with a molecular mass of 120-125 kDa and the carbohydrate moiety makes up approximately 6% (w/w) of the protein. The amino acid composition displays an important amount of acidic/amide and hydroxy amino acid residues and a low content of basic residues. The enzyme activity is markedly affected by the ionic strength of the medium and the rate-pH curve was shifted towards higher pH values in the presence of added salt. Acid beta-galactosidase is capable of catalysing transgalactosylation reactions. The yields of galactosylation of hydroxy amino acid derivatives, catalysed by the enzyme in the presence of lactose as the glycosyl donor, were higher than those reported previously with conventional sources of beta-galactosidases. In addition, the pH optimum is different for the hydrolysis (pH 3.2) and transgalactosylation (pH 5.0) reactions. On the basis of this work, the enzyme could be used as a tool in the structural analysis of D-galactose-containing oligosaccharide chains, as well as for the synthesis of glycoconjugates.
从玛瑙螺消化液中分离出一种酸性β-半乳糖苷酶，并通过阴离子交换、凝胶过滤和羟基磷灰石色谱法将其纯化至同质。这种酶是可溶的，如同胞质β-半乳糖苷酶一样，在酸性pH下发挥作用，类似于溶酶体酶，但与其他可溶性动物β-半乳糖苷酶不同的是，它对β-D-半乳糖基残基具有高度特异性。此外，它切割β1-4键的速度比β1-3和β1-6键快得多。该酶是一种单体糖蛋白，分子量为120 - 125 kDa，碳水化合物部分约占蛋白质的6%（w/w）。氨基酸组成显示出大量的酸性/酰胺和羟基氨基酸残基，碱性残基含量较低。酶活性受到介质离子强度的显著影响，在添加盐的情况下，速率-pH曲线向更高的pH值移动。酸性β-半乳糖苷酶能够催化转半乳糖基化反应。在以乳糖作为糖基供体的情况下，该酶催化羟基氨基酸衍生物的半乳糖基化产率高于先前报道的传统β-半乳糖苷酶来源。此外，水解反应（pH 3.2）和转半乳糖基化反应（pH 5.0）的最适pH不同。基于这项工作，该酶可作为分析含D-半乳糖寡糖链结构以及合成糖缀合物的工具。
