Compartmentation of the CHO-K1 metabolism and the fate of extracellular metabolites. Net fluxes are indicated on the gray arrows in units of mmol product/ (L cell × h), and reversibility parameter defined as reverse flux/net flux is shown in the square brackets (n.d. = not determined). The thickness of the gray arrows is proportional to the forward flux (=reverse flux + net flux), and shown qualitatively for the fluxes with variable reversibility. Net flux direction is shown by the black arrow heads. Amino acids catabolism is represented as the sum of the differences between amino acid uptake flux and flux required for protein production, reported to the metabolite derived from catabolism. Subscripts meaning: ex – extracellular; c – cytosolic; m – mitochondrial. Abbreviations: AAex1 – isoleucine, leucine, lysine, phenylalanine, tyrosine catabolized to acetyl-CoA; AAex2 - isoleucine, methionine, phenylalanine, threonine, tyrosine, valine catabolized to fumarate and succinate; AAex3 – arginine, histidine, proline catabolized to glutamate; AcoA – acetyl CoA; ALA – alanine; ASN – asparagine; ASP – aspartate; CIT/ICI – citrate/isocitrate; GLN – glutamine; GLU – glutamate; GLY – glycine; MAL – malate; PYR – pyruvate; SER – serine.