The regulation of glutaminolysis and citric acid cycle activity during mammalian cell cultivation

Glutaminolysis and citric acid cycle generate carbon sources and cellular energy in dependence of the biosynthesis needs. We here introduce a concept which combines a simple and practicable kinetic description of both pathways with a cell growth model to elucidate the influence of extracellular substrates, transport mechanisms and enzyme regulation on the metabolic activity. The derived model focuses on key reactions and replaces complex cellular mechanisms with growth-dependent functions. The uptake of glutamine and glutamate explains, in combination with cell size variations, a peak-like increase in intracellular metabolite pools at day two after inoculation of cells. Additional regulation of citric acid cycle enzymes prevents the degradation of metabolites during stationary growth phase even under substrate limitation. This work reveals possible ways to improve the biotechnological process of cell cultivation and provides a deeper understanding of glutaminolysis and citric acid cycle activity regulation in mammalian cells.