Study on the role of tyrosine side-chains at the active centre of emulsin β-d-glucosidase

László Kiss, Ibolya Kóródi, Pál Nánási
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引用次数: 4

Abstract

The role of exposed tyrosine side-chains in enzyme-catalyzed reaction by sweet almond emulsion β-d-glucosidase (β-d-glucoside glucohydrolase, EC 3.2.1.21) has been studied using N-acetylimidazole as the specific reagent. The changes in activity, binding affinity and kinetic parameters (Km, V) as a result of acetylation of the phenolic hydroxyl groups have been determined. The acetylation increased the Km values of both β-glucosidase and β-galactosidase activities, whereas V remained unchanged. Similarly, the binding affinity for immobilized phenyl β-d-glucopyranoside decreased appreciably. After the removal of the acetyl groups the enzyme regained 96% of the original activity. It is concluded that the tyrosine moieties, located in the active centre of the enzyme, have both glucoside and galactoside binding functions.

乳化剂β-d-葡萄糖苷酶活性中心酪氨酸侧链作用的研究
以n -乙酰咪唑为特异性试剂,研究了暴露的酪氨酸侧链在甜杏仁乳β-d-葡萄糖苷酶(β-d-葡萄糖苷葡萄糖水解酶,EC 3.2.1.21)酶催化反应中的作用。测定了酚羟基乙酰化后活性、结合亲和力和动力学参数(Km, V)的变化。乙酰化使β-葡萄糖苷酶和β-半乳糖糖苷酶活性Km值升高,而V值保持不变。同样,固定化苯基β-d-葡萄糖吡喃苷的结合亲和力也明显降低。去除乙酰基后,酶恢复了原来96%的活性。结果表明,位于酶活性中心的酪氨酸部分具有糖苷和半乳糖苷结合功能。
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