Environmental Engineering Reference
In-Depth Information
Figure 8 Channels involved in substrate/product transfer in monofunctional CODH II Ch .
Hydrophobic channels around cluster C have been calculated with the program Hollow [ 159 ]
and are shown as blue surface. Metal clusters are depicted as spheres and colored in cyan for Ni,
orange for Fe, and yellow for S. Water molecules are represented by red spheres. Charged and
hydrophilic residues form a water channel network. The electron transfer network from clusters
C $ B' $ D is indicated by an arrow. The proton relay shuttle is compromised of histidine residues
H 96 ,H 99 , and H 102 , where the last residue has direct contact to the protein surface. The surface is
contoured in grey.
Transfer of water is guided by charged and hydrophilic residues that form a
network from the protein surface to cluster C. Protons leave the active site
through His 93 and three consecutive histidine residues (96, 99, and 102), of
which the last residue of the chain is in contact with the solvent. Electrons may
be transferred along the previously mentioned FeS-cluster cascade (C
D)
before reaching external electron acceptors. Whether cluster D is part of the
electron transfer pathway has not been established yet. If it participates in
electron transfer, electrons generated at one active site could be transferred to
the other active site of the dimer, thereby facilitating an intramolecular reductive
activation.
$
B'
$
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