Observations on the influence of glutamine,asparagine and peptone on growth and t-PA production of Chinese hamster ovary (CHO) cells

When a transfected CHO cell, that produces tissue-type Plasminogen Activator, t-PA, was transferred from a medium based on 5% Fetal Calf Serum, FCS, to a medium based on 0.8% casein peptone with variable glutamine and asparagine content, it was observed, that the growth of the cells changed from anchorage dependant to suspension culture giving more reproducible cultivations. In the FCS culture t-PA was unstable, observed as a decline in t-PA concentration after 250 h. This decline in t-PA concentration was not observed in the serum free culture, although there was a decline in productivity after 200 h. This change in production profile may be attributed to either no proteolytic attack from serum or by scavenging of proteolytic activities produced by the cells from the peptone peptides. Increasing amounts of glutamine/asparagine gave higher production of t-PA in synchrony with an increasing production of ammonia/ammonium ions. Ammonia inhibition does not seem to be a key factor for this cell line as seen with many others.