FIG 5.

(A) Schematic representation of methanol dehydrogenase (MDH)- and MaDH-mediated methylamine metabolism in M. extorquens. Primary oxidation generates free formaldehyde, which is oxidized to formate by the H₄MPT-dependent C₁ dissimilation pathway. Formate is reduced by the H₄F-dependent C₁ assimilation pathway and assimilated using the serine cycle. The reaction highlighted in red, mediated by FtfL (formyl-tetrahydrofolate ligase), is unique to this topology. (B) Schematic representation of chloromethane metabolism in M. extorquens CM4. Primary oxidation produces H₄F derivatives, using an H₄F-dependent C₁ dissimilation pathway, and completely bypasses formaldehyde production. Methylene tetrahydrofolate (CH₂=H₄F) is assimilated using the serine cycle. The reactions highlighted in orange, which are catalyzed by enzymes of the H₄F-dependent C₁ dissimilatory pathway (MetF, FolD, and PurU), are unique to this topology. (C) Schematic representation of the metabolic network involved in methylamine growth if the end product of the N-methylglutamate pathway is formaldehyde. The condensation of formaldehyde and H₄F to form CH₂=H₄F, highlighted in blue, is unique to this topology. (D) Schematic representation of the metabolic network involved in methylamine growth if the end product of the N-methylglutamate pathway is CH₂=H₄F. CH₂=H₄F enters the H₄MPT-mediated C₁ assimilation pathway either by dissociation to formaldehyde (I) or by a direct cofactor switch (II). These two alternate reactions, indicated by green arrows, are unique to this topology.