Ammonium ion accumulation in mammalian cell culture media causes toxicity which inhibits cell growth and productivity. To reduce the level of the accumulated ammonium ion, carbamoyl phosphate synthetase I (CPS I) and ornithine transcarbamoylase (OTC) were used, which catalyze the first and second steps of the urea cycle in the liver. To examine the effects of overexpressed CPS I and OTC genes on the concentration of the ammonium ion in culture media, the two genes were introduced into Chinese hamster ovary (CHO) dhfr-cells. The CPS I expressing cell lines (CPS I-CHO) and both CPS I and OTC expressing cell lines (CPS I/OTC-CHO) were confirmed at the mRNA level and analyzed in terms of the cell growth and the accumulation of ammonium ion in culture media. The accumulation of ammonium ion was ≃25-33% less in CPS I/OTC-CHO than in either CPS I-CHO or the vector-control cell lines. Interestingly however, the cell growth was ≃15-30% faster in both CPS I-CHO and CPS I/OTC-CHO than in the control cell lines. Forced expression of urea cycle enzymes in the CHO cells revealed that both the expression of CPS I and OTC can reduce the accumulation of ammonium ion in the culture media. (C) 2000 Elsevier Science B.V.
- Ammonium ion
- CHO cells
- Carbamoyl phosphate synthetase
- Ornithine transcarbamoylase
- Urea cycle
ASJC Scopus subject areas
- Applied Microbiology and Biotechnology