Effects of ammonia and lactate on growth, metabolism, and productivity of BHK cells

The aim of the present work was to study the effect of ammonia and lactate on growth, metabolism, and productivity of BHK cells producing a recombinan t fusion protein. Results show that cell growth was reduced with the increa se in ammonia or lactate: k(1/2) of 1.1 mM and 3.5 mM for stirred and stati onary cultures, respectively, for ammonia and of 28 mM for both stationary and stirred cultures for lactate, were obtained. The cell-specific consumpt ion rates of both glucose (q(Glc)) and glutamine (q(Gln)) increased, wherea s that of oxygen (q(O2)) decreased, with the increase in ammonia or lactate concentrations. The cell-specific production rates of lactate (q(Lac)) inc reased with an increase in ammonia concentration; similarly for the cell-sp ecific production rates of ammonia (q(Amm)), which also increased with an i ncrease in lactate concentration; on the other hand, both q(Lac), and q(Amm ) markedly decreased when lactate or ammonia concentrations were increased, respectively; lactate was consumed at lactate concentrations above 30 mM a nd ammonia was consumed at ammonia concentrations above 5 mM. In vivo (PNMR )-P-31 experiments showed that ammonia and lactate affect the intracellular pH, leading to intracellular acidification, and decrease the content in ph osphomonoesters, whereas the cell energy state was maintained. The effect o f lactate on cell growth and q(Gln) is partially due to osmolarity, on q(Gl c) and q(Amm) is entirely due to osmolarity, but on q(Lac) is mainly due to lactate effect per se. An increase in ammonia from 0 to 20 mM induced a 50 % reduction in specific productivity, whereas an increase in lactate from 0 to 60 mM induced a 40% decrease. (C) 2000 Elsevier Science Inc. All rights reserved.