Figure 2.
The network composed of reactions exhibiting variable flux in response to changing ATP demand (see also Figs. 1 and 3). Colors correspond to the description in Figure 1; reactions shown with broken lines indicate those that at some level of ATP demand carry no flux (see Fig. 3). The reactions shown in black are also included, although their fluxes do not respond to changing ATP demand (in these solutions); they form a single connected block whose start and end points are in the block of variable reactions. The purpose of this diagram is to illustrate relationships between the reactions of primary metabolism, and to this end a number of simplifications have been made: metabolite names are the common abbreviations, not Biocyc identifiers; the transhydrogenase reaction at the top of the figure is composed of the NAD and NADP variants of icosanoyl-CoA synthase (EC 2.3.1.119) operating in opposed directions (see “Discussion”); the oxidative limb of the oxidative pentose phosphate pathway is shown as a single lumped reaction; and CO2, oxygen, currency metabolites, the electron transport chain, and oxidative phosphorylation are omitted. Additional fixed outputs from the system are not shown (see “Discussion”).