beta-D-Fucosidase, beta-D-glucosidase and beta-D-galactosidase activities from bovine liver are associated in a single peak in isoelectric focusing. The isoelectric point is 4.35 for all these activities, suggesting that they are catalyzed by the same enzyme. 2. This enzyme shows the optimal pH in the range 4.5-6.5 for all the above mentioned activities. 3. The Km and Vmax are 0.26 mM and 31 mU mg-1, 0.10 mM and 24 mU mg-1, and 0.30 mM and 20 mM mg-1 for the p-nitrophenyl-fucoside, -glucoside and -galactoside, respectively. The glucoside derivative is the best substrate, with a Vmax/Km value of 0.24 ml . mg-1 . min-1. 4. The Lineweaver-Burk profiles are convex upward in most cases, suggesting a substrate-activation model, and the presence of more than one binding site in the enzyme. 5. The Ki for all the activities were determined with D-fucose, glucose and galactose as inhibitors. D-Fucose is the strongest inhibitor. The inhibition is competitive in all cases.
摘要
牛肝中的β-D-岩藻糖苷酶、β-D-葡萄糖苷酶和β-D-半乳糖苷酶活性在等电聚焦中集中于单一峰。所有这些活性的等电点均为4.35，表明它们由同一种酶催化。2. 该酶对上述所有活性而言，在4.5 - 6.5的pH范围内表现出最佳活性。3. 对硝基苯基岩藻糖苷、对硝基苯基葡萄糖苷和对硝基苯基半乳糖苷的Km和Vmax分别为0.26 mM和31 mU mg-1、0.10 mM和24 mU mg-1以及0.30 mM和20 mM mg-1。葡萄糖苷衍生物是最佳底物，Vmax/Km值为0.24 ml·mg-1·min-1。4. 在大多数情况下，Lineweaver-Burk曲线向上凸出，提示底物激活模型以及该酶中存在不止一个结合位点。5. 以D-岩藻糖、葡萄糖和半乳糖作为抑制剂测定所有活性的Ki。D-岩藻糖是最强的抑制剂。在所有情况下抑制作用均为竞争性。
