ADAPTATION OF MAMMALIAN-CELLS TO NONAMMONIAGENIC MEDIA

Although glutamine is used as a major substrate for the growth of mamm alian cells in culture, it suffers from some disadvantages. Glutamine is deaminated through storage or by cellular metabolism, leading to th e formation of ammonia which can result in growth inhibition. Non-ammo niagenic alternatives to glutamine have been investigated in an attemp t to develop strategies for obtaining improved cell yields for ammonia sensitive cell lines. Glutamate is a suitable substitute for glutamin e in some culture systems. A period of adaptation to glutamate is requ ired during which the activity of glutamine synthetase and the rate of transport of glutamate both increase. The cell yield increases when t he ammonia accumulation is decreased following culture supplementation with glutamate rather than glutamine. However some cell lines fail to adapt to growth in glutamate and this may be due to a low efficiency transport system. The glutamine-based dipeptides, ala-gln and gly-gln can substitute for glutamine in cultures of antibody-secreting hybrido mas. The accumulation of ammonia in these cultures is less and cell yi elds in dipeptide-based media may be improved compared to glutamine-ba sed controls. In murine hybridomas, a higher concentration of gly-gln is required to obtain comparable cell growth to ala-gln or gln-based c ultures. This is attributed to a requirement for dipeptide hydrolysis catalyzed by an enzyme with higher affinity for ala-gln than gly-gln.