Objective: To verify whether the enzymatic activity of kynureninase (KYNU) could be changed by the Arg188Gln (G/A) mutation. Methods: The total RNA of human hepatic tissue was extracted and the KYNU gene cDNA was amplified by RT-PCR. Primers were designed according to the sequences around the site Arg188Gln of KYNU gene and the Arg188Gln (G/A) mutant KYNU cDNA was generated by site-directed mutagenesis. Both the wild-type and mutant-type KYNU genes were subcloned into pcDNA vectors and the recombinant plasmids were constructed. After being transfected into human embryonic kidney 293 (HEK293) cells, the expression of KYNU recombinant plasmids were assessed by Western blot. The enzymatic activities of KYNU were detected by high performance liquid chromatography (HPLC). Results: The KYNU enzyme activities were expressed in both wild and mutant HEK293 cells. Michaelis constants (Km) of the wild and mutant KYNU were (9.833±0.513) μmol/L and (29.900±0.265) μmol/L, respectively (P<0.05). The maximum velocities (Vmax) of the wild and mutant KYNU were (0.700±0.096) nmol·mg-1·min-1 and (0.084±0.003) nmol·mg-1·min-1, respectively (P<0.05). Conclusion: Arg188Gln (G/A) mutation can decrease the enzymatic activity of KYNU.
目的: 验证犬尿氨酸酶（KYNU）Arg188Gln（G/A）突变能否改变KYNU的活性。
方法: 抽提人肝脏细胞的总RNA，通过RT-PCR法获得 KYNU基因全长cDNA，以 KYNU基因Arg188Gln位点附近序列为模板设计定点突变引物，完成Arg188Gln（G/A）的定点突变，将突变型和野生型 KYNU基因克隆到pcDNA载体质粒中，获得野生型和突变型pcDNA-KYNU重组表达质粒，经酶切鉴定和测序验证后转染HEK293细胞，蛋白质印迹法检测KYNU在细胞中的表达，用高效液相色谱法检测HEK293细胞的KYNU活性。
结果: 野生型和突变型pcDNA-KYNU重组质粒在HEK293细胞中均能表达有活性的KYNU，KYNU的米氏常数分别为（9.833±0.513）μmol/L和（29.900±0.265）μmol/L，最大酶促反应速率分别为（0.700±0.096）nmol·mg -1·min -1和（0.084±0.003）nmol·mg -1·min -1，差异均有统计学意义（均 P < 0.05）。
结论: Arg188Gln（G/A）突变可以减弱KYNU的活性。