中文摘要：

γ-谷氨酰转肽酶（GGT）是生物体内谷氨酰循环的关键酶,在生物有机合成领域具有重要的应用价值。今建立了大肠杆菌和枯草芽孢杆菌GGT的克隆、重组及诱导表达方法。在此基础上,分别考察了重组大肠杆菌GGT（rE_GGT）和重组枯草芽孢杆菌GGT（rB_GGT）的催化特性和稳定性。结果表明,rE_GGT对供体对硝基苯胺（GpNA）的亲和力（Km）优于rB_GGT,但rB_GGT的催化常数（kcat）高达3.48×105 s-1,是rE_GGT的20倍。稳定性研究表明,rE_GGT在pH 6-9和T〈45℃条件下的稳定性明显优于rB_GGT;但当温度超过45℃时,rB_GGT的稳定性更佳。通过对rE_GGT和rB_GGT的氨基酸组成及其大、小亚基界面相互作用力的分析表明,rE_GGT大小亚基间疏水键的数目明显多于rB_GGT,有助于稳定其四级结构,使其在中低温下具有良好的稳定性;而rB_GGT氨基酸组成中荷电残基和芳香族残基的比例较高,可有效维持其二级结构的稳定性。

英文摘要：

The enzyme T-glutamyltranspeptidase is the key enzyme involved in glutathione metabolism, andhas wide applications in biocatalysis. In this paper, the GGTs from Escherichia coli and Bacillus.subtilis werecloned, recombined and expressed. The catalytic properties and stabilities of the recombined GGTs from E. coli（rE_GGT） and B. subtilis （rB_GGT） were investigated, respectively. The results show that, although the affinityof rE GGT toward GpNA （Km） is higher than that of rB_GGT, the catalytic constant of rB_GGT （kcat） is as highas 3.48x10^5 s-l, which is 20 folds as high as that ofrE_GGT. Stability studies reveal that rE_GGT is more stablethan rB_GGT under the condition of pH 6-9 and T〈45℃. While the temperature is above 45 ℃, rBGGT ismore stable. The studies for the amino acid composition and subunit interface interactions of r_EGGT andrB_GGT show that the rE_GGT has more hydrophobic bonds to help stabilizing its quaternary structure and tomake it more stable under moderate temperature. The percentages of charged and aromatic residue in rB_GGTare higher than that in rE_GGT, which is helpful to improve the stability of its secondary structure.