oxidation and dihydrogen formation under fermentative growth conditions [141,
148–151]. The system comprises two enzymes, the cytoplasmatic Mo-FDH (described above) and a membrane-bound, cytoplasm-faced nickel/iron-containing
hydrogenase (Ni/Fe-Hase); FDH oxidises formate to CO 2 and the resulting reducing
equivalents are transferred, through three Fe/S proteins, to the Ni/Fe-Hase that
reduces protons to dihydrogen (Fig. 7).
A different rearrangement of the same basic features (FDH plus Hase) is found in
cytoplasmatic dihydrogen-dependent FDHs (better denominated as CO 2 reductases),
that physiologically catalyse the reduction of CO 2 to formate with the simultaneous
SeCys 196
His 197
Arg 446
C
A
B
Mo
FS0
FS1
FS4
FS2
FS3
b P
b C
cardiolipin
membrane
periplasm
cytoplasm
Fig. 5 E. coli formate dehydrogenase N. A Three-dimensional structure view. B Arrangement of
the redox-active centres shown in the same orientation (but not same scale) as in (A).
C Molybdenum catalytic centre of oxidised enzyme. The structures shown are based on the PDB
file 1KQF [119] (a helices and b sheets are shown in red and cyan, respectively)
Carbon Dioxide Utilisation—The Formate Route
41