中国生物工程杂志

Induced by lactose, the recombinant Candida utilis uricase was expressed in the E.coli JM109(DE3) that carried the PET-uricase expression plasmid. The crude extraction was processed by the following purification procedures including ammonium sulfate precipitation, anion-exchange chromatography and gel filtration chromatography and the recombinant uricase with 95% purity could be obtained. Using HPLC and reduced SDS-PAGE, the native molecular weight of this enzyme and the apparent molecular weight of its subunit were determinied as 130 kDa and 33 kDa. The (mPEG)2-Lys-NHS of 20 kDa was used to modify the purified uricase and the study on zymological properties of uricase before and after modification was carried on. The results showed that the optimum pH of PEG modified uricase and native uricase were pH 7.5 and pH 8.5 respectively and both of them had good pHstability from pH 6 to 10; both of the two had the same optimum temperature of 40℃, but the thermal stability and the ability of antitrypsin hydrolysis of the pegylated enzyme were much better than those of native enzyme; the modified uricase retained 87.5% of the enzymatic activity of native uricase; under each optimum condition, the determined Km of uricase before and after pegylation were 3.91×10-5 mol/L  and 3.57×10-5 mol/L respectively. These findings may provide some information for deep investigation of structure and function of pegylated uricase.