PRODUCTION OF A MEMBRANE-BOUND PROTEIN, THE HUMAN GAMMA-GLUTAMYL-TRANSFERASE, BY CHO CELLS CULTIVATED ON MICROCARRIERS, IN AGGREGATES AND IN SUSPENSION

Recombinant Chinese Hamster Ovary (CHO) cells, engineered for the prod uction of human gamma-glutamyl transferase (GGT), have been grown on C ytodex 1 microcarriers, as aggregates, or as single cells in suspensio n after adaptation. GGT is a membrane bound enzyme which was not secre ted during the culture period. The maximal enzyme activity was found t o be directly related to the achieved maximal cell density. Culture of CHO on microcarriers yielded the fastest growth, with a specific grow th rate of 0.04 h(-1), the highest cell density (near 1.3 x 10(6) cell s ml(-1)), and the highest enzyme activity around 300 mU ml(-1), which corresponded to a specific cellular level of 20 mU 10(-5) cells. GGT could also be produced by growing CHO cells in suspension as single ce lls or as aggregates. Under these conditions, however, the specific CH O growth rate was significantly slower and the GGT level per cell was divided by a factor 6. Glowing CHO cells without microcarriers also re sulted in differences in cell metabolism, with a higher conversion yie ld of glutamine into ammonia, and a higher cell lysis. The catalytic k inetic constants of the enzyme were found identical for the three cult ure systems.