 Solution

Important unlisted candidates include ATP synthase, the mitochondrial phosphate carrier, and succinate dehydrogenase itself, which supplies electrons from succinate to ubiquinone. Availability or transfer of ubiquinone and cytochrome c, and associated transport or metabolite constraints, may also need explicit treatment depending on how the pathway is grouped. ATP synthesis, phosphate supply and substrate oxidation have not all been individually represented. Respiratory complex I is absent from the table but is not required for the direct forward route from succinate into the ubiquinone pool; its omission alone does not account for missing control of that route.