Carbon Monoxide. Toxic Gas and Fuel for Anaerobes and Aerobes: Carbon Monoxide Dehydrogenases - The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment - page 56

H þ
ð

CH 3 -Co III ðÞ CoFeSP þ CO þ CoASH Ð CH 3 CO ðÞ SCoA þ Co I ðÞ CoFeSP þ

Þ

2

Based on subunit composition, Lindahl et al. [ 74 , 109 ] proposed four classes
of Ni,Fe-containing CODHs, of which classes I, II, and III are bifunctional
(Figure 11 ). Class I and II enzyme complexes, which are also termed acetyl-CoA
decarbonylase/synthase (ACDS), are found in methanogenic archaea. Class I
enzymes are used by obligate autotrophic methanogens like Methanobacterium
thermoautotrophicum to generate acetyl-CoA from CO 2 , CoASH, and H 2 [ 110 ].
Class II enzymes are used by facultative chemo-autotrophic methanogens like
Methanosarcina frisia and M. thermophila , which are able to catabolize acetate
generating CO 2 , CoASH, and a methyl group bound to tetrahydrosarcinapterin, a
tetrahydrofolate analogue used by archaea [ 38 ]. Class III CODH/ACS is found in
acetogens [ 26 ]. As illustrated in Figure 11 , the monofunctional CODH homodimers
(class IV) consist of one subunit ( ʲ ), which is homologous to the CODH compo-

nents of class I/II (subunit ʱ ) and class III (subunit ʲ ). The class III enzymes consist

of two autonomous proteins, an ( ʱʲ ) 2 dimer of dimers (ACS/CODH), and a ʳʴ

heterodimer (CoFeSP). The ʲ

subunit of class I/II, but lacks a 30 kDa region at the N-terminus. CoFeSP is
homologous to the

ʱ subunit (ACS component) is homologous to the

ʳ and ʴ subunits of the archaeal enzyme complex (class I/II),

Figure 11 Subunit composition of Ni,Fe-containing CODHs. Connected circles indicate
multiprotein complexes consisting of the corresponding subunits. Homology is indicated by
arrows. The figure was adapted from Lindahl [ 74 ]. Details are given in the text.