FIG 5.
Hypothesized metabolic pathway of methylphosphonate in Prochlorococcus strain MIT9301. Methylphosphonate (MPn) is transported across the cell membrane (gray lines) by the PtxABC ATP-binding cassette transport system. MPn carbon is hydroxylated by PhnY, an Fe(II)/α-ketoglutarate-dependent dioxygenase, forming hydroxymethylphosphonate (HMPn). PhnZ, an Fe(II)-dependent oxygenase of the histidine-aspartate hydrolase superfamily, completes the oxidation of MPn to formate and inorganic phosphate (Pi). Formate can be excreted through the cell membrane by simple diffusion or by an unknown transporter. Formate is also assimilated by PurT to form FGAR (formyl-glycinamide ribose). FGAR is further modified in the synthesis of purine ribonucleotides.