Fig 1.

Scheme of the energy metabolism of C. acidurici growing on uric acid. The scheme highlights the proposed role of the electron-bifurcating formate dehydrogenase. Fd, ferredoxin; H₄F, tetrahydrofolate; Xdh, xanthine dehydrogenase; Fhd/Hyl, electron-bifurcating formate dehydrogenase; methylene-H₄F DH, 5,10-methylene-H₄F dehydrogenase; GCS, glycine cleavage system; PFOR, pyruvate:Fd oxidoreductase. The reduced ferredoxin required for uric acid reduction is regenerated in the Fdh/Hyl and PFOR reactions.