RESUMO
Using the character of natural aggregation of CHO cells, and an ultrasonic and sedimentation column combined perfusion system to promote cells aggregation and retention into bioreactor,recombinant CHO cell strain MK3-A2 was cultured,which could secrete rhTNK-tPA, by a serum-free perfusion culture system. The culture periods in this two experiments were as long as 77 and 110 days respectively. The cells density reached 2?107 cells /ml. The average volumetric productivity of rhTNK-tPA was 89 mg/L?d, and the highest one was 216mg/L?d.The cells aggregation rate was approximately 90%, and the diameters of most of them were 285～570?m. During the perfusion culture the cells retention rate almost kept in 95% and the viability of cells was more than 85%.Thus, it means that aggregation culture with such perfusion system could be used to scale up produce biopharmaceuticals instead of microcarrier culture system.
RESUMO
The only difference of primary structure between single-chain prourokinase (pro-UK or scu-PA) and two-chain urokinase (UK or tcu-PA) is the cleavage of a single peptide bond (Lys158-Ile159) and transform scu-PA into its active two-chain form. A 13-peptide (Thr-Leu-Arg-Pro-Arg-Phe-Lys-Ile-Ile-Gly-Gly-Glu-Cys), which spans the cleavage peptide bond, was synthesized and linked to KLH (Keyhole limpet hemocyanin). The Balb/c mice were immunized by the conjugated protein with proper adjuvant. According to the Kohler and Milstein's methods, a hybridoma cell line G7 secreting monoclonal antibody specific for scu-PA was obtained. The anti-scu-PA McAb, purified from the supernatant of porous microcarrier hybridoma cell culture, was conjugated to CNBr-activated Sepharose 4B to prepare an immuno-affinity chromatography column. The u-PA was purified only by this affinity column from the supernatant of cultivating the u-PA-producing recombinant CHO cell, the u-PA recovery ratio is 90.4%, the purification factor was about 50, with the specific activity of 1.2 x 10(5) IU/mg, the scu-PA ratio in the u-PA product was 96.3%. Compared to immuno-affinity chromatography, the 3-step process for purifying u-PA (cation-exchange column, gel filtration column and benzamidine affinity column) has a u-PA recovery ratio of about 65%, with a specific activity of 1.0 x 10(5) IU/mg, and an scu-PA ratio of about 90%. These results showed that immuno-affinity chromatography is simple to recover u-PA and effective to separate scu-PA from tcu-PA.