Dynamic modeling of the intracellular availability of phosphoenolpyruvate with respect to the specific rate of fructose uptake. Dynamic modeling of the intracellular availability of phosphoenolpyruvate with respect to the specific rate of fructose uptake. The plots indicate the level of phosphoenolpyruvate (PEP, y axis) while varying the specific rate of fructose uptake (qS, k17 in the network shown in Fig. 4, x axis) for the wild-type (WT) Pseudomonas putida KT2440 strain (A) and its Δcra derivative (B). Black lines (arrows pointing to the right) show the state of PEP in the system while k17 increases from an initial state without fructose in the medium (far left). Red lines (arrows pointing to the left) show the state of PEP in the system while k17 decreases from the final state (far right). The OFF and ON states of the system are indicated in the graphics, and the architecture of the network is shown on top of the plots in terms of inverters (connecting PEP and fructose through the regulatory action exerted by Cra). The yellow dot indicates the experimentally measured values for the intracellular PEP level and k17. The shadowed areas in the plots indicate what would happen if the cells were hypothetically overloaded with fructose (i.e., beyond the physically possible limits determined experimentally). As shown in the diagrams, the level of available PEP would decrease, as it would be consumed right away to mediate fructose transport. Max Chavarría et al. mSystems 2016; doi:10.1128/mSystems.00154-16