The N-terminal loop may be involved in the determination of the kinetic mechanism, i.e., an ordered or a random model, and the C-terminal loop may contribute to the better CO2-reducing activities of bacterial FDHs than those of eukaryotic FDHs. To understand the amino acid differences of FDHs at molecular level, the structural alignment of TsFDH and CbFDH was performed. The structure of TsFDH was modeled using SWISS-MODEL homology modeling. The holo-crystal structure of NAD-dependent FDH from Pseudomonas sp. 101 was used as a template for homology modeling of TsFDH structure because the C-terminal loop, which covers the substrate channel, is only present in the holo-structure: the loop may be largely fluctuated in the apo-structure. The Nterminal loop covers a significant part of the enzyme, and some amino acids in the loop interact with other amino acids of the subunit or the other chain in a dimeric form. However, the N-terminal loop does not have direct interactions with the substrate binding pocket. It was reported that PdFDH has a narrow substrate channel, and Arg284 on the wall of the substrate channel provides conformational mobility for binding and delivery of substrates. In addition, Arg284 has close contacts with an inhibitor i.e. azide in the ternary complex structure. Based on this structure information of PdFDH, it can be speculated that upon sequential binding of cofactor and substrate the C-terminal loop can be formed and then, contribute to conformational changes of the substrate channel including Arg284 for enzyme catalysis. The C-terminal loop, which is not present in the structure of CbFDH, in the modeled structure of TsFDH also covers the substrate binding channel, including Arg284. This structural feature of TsFDH may be associated with CO2 accessibility or binding to the active site given that the kinetics data revealed that TsFDH exhibited a better KB value than CbFDH. However, we do not yet know whether the loops play important roles in CO2 binding or catalytic motion in the bacterial FDHs. Although there are many crystal structures and abundant TC-E 5006 biochemical information on NAD-dependent FDHs, the functions of these loops remains Nonactin unclear. We plan to prepare a TsFDH Cterminal loop deletion mutant to test the hypothesis. In summary, five FDHs with acidic optimum pH identified from biochemical data were tested for CO2 reduction. The superior CO2-reducing activity of TsFDH was confirmed by enzyme kinetics and formate production from CO2 gas.We propose that TsFDH is an alternative to the conventional CO2-reducing biocatalyst CbFDH. However, further experiments, including protein engineering and the development of NADH-regeneration systems, will be required to improve the CO2-reducing efficiency of TsFDH.