化学修饰法表征Bacillus smithii T7产耐热菊粉酶催化活性中心的必需氨基酸残基

Characterization of Key Amino Acid Residues in Active Sites of Inulinase from Bacillus smithii T7 by Chemical Modification

采用化学修饰法研究了史氏芽胞杆菌Bacillus smithiiT7产耐热菊粉酶活性中心氨基酸残基,发现该酶活性中心存在一个组氨酸残基和一个谷氨酸(或天冬氨酸)残基.修饰前后的酶动力学参数变化表明组氨酸残基参与了底物的结合和催化过程,而谷氨酸(或天冬氨酸)的羧基亲核攻击促使底物分解.邹氏作图法证明酶活性中心存在两个必需的色氨酸残基,荧光和圆二色光谱研究表明色氨酸残基在酶的催化和酶的耐热性方面起重要作用.

The amino acid residues participating in the active site of the extracellular thermostable endo-inulinase from Bacillus smithii T7 were investigated by chemical modification. The results show that there are one histidine residue and one carboxylate residue in the active site. The kinetic study of the enzyme before and after modification by diethylpyrocarbonate and carbodiimide showed that one histidine residue might play a key role in substrate binding and catalysis, and one carboxylate residue located in the active site may act as a nucleophile base for the cleavage of substrate. The Tsou＇s plot analysis indicated that the inactivation of the enzyme is dependent upon the modification of two essential tryptophan residues. Fluorescence and circular dichroism spectroscopy assays and the thermal inactivation study of the modified enzyme also confirmed that tryptophan residues play an important role in the catalysis and thermal stability of the inulinase.