Relative amounts predicted by model, on a mass basis, shown for each pathway derived from the 3HP/4HB cycle. The pathways are (A) acetyl-CoA autotrophic, (B) succinate autotrophic, (C) succinate heterotrophic (via acetyl-CoA), and (D) 3HP heterotrophic (via acetyl-CoA). Enzyme abbreviations: Acetyl-CoA/propionyl-CoA carboxylase (ACC), Malonyl-CoA/succinyl-CoA reductase (MCR), Malonic semialdehyde reductase (MSR), 3-Hydroxypropionyl-CoA synthetase (HPCS), 4-Hydroxybutyryl-CoA synthetase (HBCS), 3-Hydroxypropionyl-CoA dehydratase (HPCD), Acryloyl-CoA reductase (ACR), Methylmalonyl-CoA epimerase (MCE), Methylmalonyl-CoA mutase (MCM), Succinic semialdehyde reductase (SSR), 4-Hydroxybutyryl-CoA dehydratase (HBCD), Bifunctional crotonoyl-CoA hydratase/(S)-3-hydroxybutyryl-CoA dehydrogenase (CCH/HBCD), Acetoacetyl-CoA β-ketothiolase (AACT), Succinic semialdehyde dehydrogenase (SSADH).