嗜碱细菌环状糊精葡糖基转移酶的纯化和性质

嗜碱细菌52—2除去菌体的培养液经硫酸铵沉淀和DEAE－纤维素离子交换柱层析，得到凝胶电泳均一的环状糊精葡糖基转移酶，纯化了11.5倍，酶活力回收为5.7％。用浓度梯度PAGE测分子量为151700。酶反应最适温度为65℃，50℃以下比较稳定。酶反应最适pH为7．0，在6．0～9.0范围内稳定。Zn²⁺、Hg²⁺、Pb²⁺、Al³⁺、Cu²⁺、Ag⁺和Fe²⁺强烈抑制酶活力。紫外光谱在270nm和244nm处分别有最大和最小吸收。荧光光谱的最大激发波长和发射波长分别为283nm和335nm。用NBS、NEM、NAI、DEP和EDC对酶进行了化学修饰，初步推测组氨酸和色氨酸残基可能为酶活力必需基因，羧基与酶活力有一定关系。

PURIFICATION AND CHARACTERIZATION OF CYCLOMALTODEXTRIN GLUCANOTRANSFERASE FROM ALKALIPHILIC BACTERIA

A cyclomaltodextrin glucanotransferase from alkaliphilic bacteria was purified to PAGE homogenous by ammonium sulfate precipitation and DEAE-cellulose DE-52 chromatography with 11.5 fold purification and 5.7% recovery. Mr estimated with concentration gradient PAGE was 151,000. The optimum conditions for activity were pH 7.0, temperature 60 degrees C, stable in the range 6.0-9.0 and below 50 degrees C. The enzyme activity was activated by salicin and maltitol, slightly inhibited by Sn2+, Mn2+, inositol and pullulan, strongly inhibited by Ag+, Cu2+, Al3+, Fe2+, Pb2+, Hg2+ and Zn2+. The maximum absorption was at 270 nm in ultraviolet spectrum, the maximum emission wavelenghth in the excitation spectrum was 283 nm, the maximum emission spectrum determined at 283 nm was 335 nm. The effects of some protein modification reagents on the CGTase activity have been studied. Histidine and tryptophan residues may be essential for activity, carboxyl groups might have some effects on the activity.