Scheme of C₁ metabolism of the methylotroph Methylobacterium extorquens AM1.

The bacterium oxidizes methanol to formaldehyde that is condensed with a tetrahydromethanopterin and further oxidized to formate. Formate reacts with tetrahydropterin and formyl-tetrahydrofolate is further converted to methylenetetrahydrofolate (part 1 of metabolism). The serine cycle is used for the assimilation of formaldehyde plus bicarbonate (part 2). Acetyl-CoA assimilation and conversion to glyoxylate proceeds via the ethylmalonyl-CoA pathway (part 3). The main biosynthetic outputs from these pathways are indicated. Enzymes: 1, serine hydroxymethyl transferase; 2, serine-glyoxylate aminotransferase; 3, hydroxypyruvate reductase; 4, glycerate kinase; 5, enolase; 6, phosphoenolpyruvate carboxylase; 7, malate dehydrogenase; 8, malate-CoA ligase (malate thiokinase); 9, L-malyl-CoA/β-methylmalyl-CoA lyase; 10, β-ketothiolase; 11, acetoacetyl-CoA reductase; 12, crotonase (R-specific); 13, crotonyl-CoA carboxylase reductase; 14, ethylmalonyl-CoA/methylmalonyl-CoA epimerase; 15, ethylmalonyl-CoA mutase; 16, methylsuccinyl-CoA dehydrogenase; 17, mesaconyl-CoA hydratase; 18, propionyl-CoA carboxylase; 19, methylmalonyl-CoA mutase; 20, methanol dehydrogenase. PHB, polyhydroxybutyrate, Q, quinone.