Reduction of Toxic Effect of Ammonia on Metabolism of Recombinant CHO-GS Cell

The toxic effect of ammonia on rCHO-GS cell decreased obviously due to the transfection of GS system in serum-free culture. The maximum cell density, 15.6 × 105 cells/mL, was obtained in the culture with 1.42 mmol/L ammonia. The growth of rCHO- GS cell was inhibited with an increased ammonia concentration. However, a cell density of 8.9 × 105 cells/mL was obtained when the concentration of ammonia was 12.65 mmol/L. The metabolic pathways were affected due to the decrease of the toxic effect of ammonia on rCHO-GS cell. With the increase of initial ammonia concentration from 0.36 mmol/L to 12.65 mmol/L, the yield coefficients of cell to glucose and lactate to glucose decreased. The activities of hexokinase (HK), pyruvate kinase (PK), and lactate dehydrogenase (LDH) increased by 43 %, 140 % and 25 %, respectively, indicating that the utilization of glucose increased and the glycolysis pathway was more prone to efficient energy metabolism pathway. An increased activity of glutamate-pyruvate amino- transferase (GPT) showed that the conversion from glutamate to α-ketoglutarate was shifted to glutamate-pyruvate transamination pathway. The deamination pathway was inhibited due to a decreased activity of glutamate dehydrogenase. In addition, the number of cells in G0/G1 phase increased and the specific productive rate of recombinant protein increased by 2.1-fold with the increase of initial ammonia concentration from 0.36 mmol/L to 12.65 mmol/L.