Convergent electron flow is built into the metabolic design of the Electron transfer pathway. The glycolytic pathways are characterized by important divergent branchpoints: phosphoenolpyruvate (PEPCK) branchpoint to pyruvate or oxaloactetate; pyruvate branchpoint to (aerobic) acetyl-CoA or (anaerobic) lactate or alanine. The mitochondrial Electron transfer pathway, in contrast, is characterized by convergent junctions: (1) the N-junction and F-junction in the mitochondrial matrix at ET-pathway level 4, with dehydrogenases (including the TCA cycle) and ß-oxidation generating NADH and FADH2 as substrates for Complex I and electron-transferring flavoprotein complex, respectively, and (2) the Q-junction with inner mt-membrane respiratory complexes at ET-pathway level 3, reducing the oxidized ubiquinone and partially reduced semiquinone to the fully reduced ubiquinol, feeding electrons into Complex III.
Reference: Gnaiger 2020 BEC MitoPathways, Gnaiger_2009_Int J Biochem Cell Biol
MitoPedia methods: Respirometry
MitoPedia topics: Substrate and metabolite