4.2 Methane Metabolism in Methane-Oxidizing Bacteria
81
Fig. 4.2 Conversion of
formaldehyde to formate
HN
N
N
H
H
N
N
CH3
O
H2
CH3
HN
OH
OH
OH
O
O
OH OH
CH2OH
HN
N
N
H
N
N
CH3
O
H2
CH3
N
OH
OH
OH
O
O
OH OH
CH2OH
dH 4 MPT
HN
N
N
H
N
N
CH3
O
H2
CH3
N
OH
OH
OH
O
O
OH OH
CH2OH
Methylene-dH 4 MPT
Methenyl-dH 4 MPT
HN
N
N
H
N
N
CH3
O
H2
CH3
HN
OH
OH
OH
O
O
OH OH
CH2OH
O
Formyl-dH 4 MPT
HCHO
NADPH + H +
NADP +
H 2 O
dH 4 MPT
HCOOH
(4) Oxidation of formate to carbon dioxide
The last step in the dissimilation pathway of methane-oxidizing bacteria is the
oxidation of formate to CO 2 . The conversion of formate to carbon dioxide is catalyzed
by the NAD-dependent enzyme FDH (EC 1.2.1.2) [82–85], which contains [2Fe–
2Fe], [4Fe–4Fe], and molybdenum as cofactors for its catalytic function. This last
step also provides electrons for the oxidation of methane to methanol [79, 86].
(5) Assimilation pathways
A mentioned above, there are two pathways for methane assimilation: the RuMP
(Fig. 4.3) and serine (Fig. 4.4) ones. Each pathway involves different reactions and
enzymes for energy production and cell replication.