Each reaction along the rTCA cycle is potentially in competition with off-target reactions that can be off-cycle or contribute to parallel rTCA cycles (Fig. ). In addition to the reactions that belong to the rTCA cycle-referred to as "main cycle" reactions throughout (green circles in Fig. )we investigated the kinetic feasibility of all competing b2f2 reactions involving each reactant along the primary rTCA cycle-referred to as "off-cycle" reactions throughout (red circles in Fig. ).