Growth experiments shown on the PhPP. (a) The three groups of experimental data displayed on the S. cerevisiae PhPP were used as an index for the time course profiles in panels (b), (c) and (d). (b) Aerobic glucose-limited growth controlled by fed-batch operation. (c) Oxidative-fermentative growth with unlimited glucose and oxygen availability. (d) Microaerobic growth with unlimited glucose and very low oxygen availability. The AGL (b) and MA (d) data sets are located on lines of optimality and as a result are stable metabolic states with only one degree of freedom (glucose for AGL and oxygen for MA). OF (c) is an unstable metabolic state with two degrees of freedom (glucose and oxygen), making it more difficult to control this type of growth condition. By perturbing the environmental conditions, cells in OF can be shifted to either AGL or MA (unpublished results).