Glutamine controls metabolic flux in bioreactor continuous cultures. The changes in the main fluxes into the TCA cycle and through glycolysis and the TCA cycle at each steady state of continuous culture (A and B). Jaa-glu is the sum of the fluxes from histidine, arginine and proline to glutamate, Jaa-succ is the sum of the fluxes from methionine, isoleucine, threonine and valine to succinyl-CoA, Jaa-accoa is the sum of the fluxes from lysine, isoleucine, leucine and tyrosine to acetyl-CoA. Jaa-CO2 was assumed to have derived from amino acid metabolism only. The relative contribution of each amino acid towards the synthesis of HCG (or any recombinant protein) is described elsewhere (Gambhir et al., 2003). (* = p < 0.05, ** = p < 0.01, *** = p < 0.001; Panels A and B, n = 5).