Hydrogenase is an active catalyst for the reversible splitting of reduced (H2) to oxidized (H+) form of hydrogen. Proteins such as FNRs (Ferredoxin) and cytochromes can act as physiological electron donors or acceptors for hydrogenase (Vignais et al., 2001). In 1931, Stephenson and Stickland were described hydrogenase. This is the major climb up for research towards efficient biohydrogen production. Biochemical, genetic, spectroscopic, crystallographic and phylogenetic analysis has been applied to understand the structure of hydrogenase. Based on this analysis hydrogenase is classified into three groups: (a). Fe-Fe, (b). Ni-Fe and (c). Fe-only. The Ni-Fe and Fe-Fe hydrogenase both contains an active site and Fe-S (iron-sulfur) cluster. The Fe-only (also known as metal-free hydrogenase) contain only an active site (not Fe-S cluster). Characteristic feature of all hydrogenase is the presence of small CO (Carbon monoxide) molecule and CN-(Cyanide) ions in their active site. This was first detected by FTIR spectroscopic analysis (Song et al., 2007).
Fe-Fe hydrogenase
Fe-Fe hydrogenase contains Fe-S clusters in their active site. It is the fastest known biological catalysts for hydrogen oxidation and reduction but highly sensitive to oxygen and get inactivated in aerobic environment. Fe-Fe hydrogenase is also reported in few eukaryotes (Vignais and Billoud, 2007).
Two classes of Fe-Fe hydrogenase are recognized:
1. Cytoplasmic, soluble, monomeric, and found in strict anaerobes such as Clostridium pasteurianum (CpI hydrogenase). This is extremely sensitive to inactivation at presence of oxygen. It has been involving in catalysis both hydrogen oxidation and reduction.
2. Periplasmic, heterodimeric, and found in Desulfovibrio sp. It could be purified aerobically, and catalyze mainly Hydrogen oxidation.
Ni-Fe hydrogenase
Ni-Fe hydrogenase possesses Ni-S and Fe-S clusters. In 2009, the reaction mechanism of Ni-Fe hydrogenase in Desulfovibrio vulgaris was proposed based on X-ray crystallography and spectroscopic data. Results were revealed that during the catalytic process, only the nickel metal ion participates in the redox reaction.
Groups and Sub-groups of Ni-Fe Hydrogenase
| [NiFe] Group | Function | Organisms in which found |
| G-1 | Membrane-bound Hydrogen uptake hydrogenase | Bacteria, archea |
| G-2 SG-2a SG-2b | Cyanobacteria uptake hydrogenases H2-sensing hydrogenase Bacteria | Bacteria Cyanobacteria, |
| G-3 SG-3a SG-3b SG-3c SG-3d | F420 reducing hydrogenase Bifunctional (NADP) hydrogenase Methyl viologen (MV) reducing hydrogenase Bidirectional NAD(P)-linked hydrogenase (NAD/NADP-reducing) | Archaea Archaea, bacteria MV-reducing archaea, bacteria Cyanobacteria, bacteria |
| G-4 | Membrane-bound hydrogen evolving hydrogenase | Hydrogen evolving archaea, bacteria |
| G-5 | High affinity hydrogenase | Actinobacteria |
Abbreviation: G-Group, SG-Sub group
Fe-only
Fe-only (or hmd hydrogenase) catalyzes the reversible reduction of methenyltetrahydromethanopterin with Hydrogen to methylenetetrahydromethanopterin (Thauer, 1998). This hydrogenase leads the pathway of methane formation from CO2 and H2, and activate only in the presence of a second substrate (methenyl tetrahydromethanopterin). This hydrogenase typically present in methanogenic arechea (Zirngibl et al., 1992).
At present, researchers were focused on improvement of hydrogenases by genetic engineering in order to get the hydrogen production rate up to thauer limit (4.0 mol Hydrogen/ mole of glucose).
References
1. Ogata, H.; Lubitz, W.; Higuchi, Y. (2009). "[NiFe] hydrogenases: structural and spectroscopic studies of the reaction mechanism". Dalton Trans 37: 7577â€"7587.
2. Song, L. C., Yang, Z. Y., Hua, Y. J., Wang, H. T., Liu, Y., and Hu, Q. M. 2007. Organometallics, 26, 2106â€"2110.
3. Thauer, R. K. (1998). Biochemistry of methanogenesis: a tribute to marjory stephenson. 1998 marjory stephenson prize lecture. Microbiology 144(Pt 9), 2377â€"2406. doi: 10.1099/00221287-144-9-2377
4. Vignais, P.M., Billoud, B. and Meyer, J. (2001). "Classification and phylogeny of hydrogenases". FEMS Microbiol. Rev. 25 (4): 455â€"501.
5. Vignais, P. M. and Billoud, B. 2007. Occurrence, classification, and biological function of hydrogenases: An overview. Chemical Reviews, 107, 4206â€"4272.
6. Zirngibl, C., van Dongen, W., Schworer, B., von Biinau, R., Richter, M., Klein, A. & Thauer, R. K. (1992) H2-forming methylenetetrahydromethanopterin dehydrogenase, a novel type of hydrogenase without iron-sulfur clusters in methanogenic archaea, Eur. J. Biochem. 208, 511-520.
About Author / Additional Info:
Research Scholar,Department of Biotechnology, NIT Raipur,
Research Interest: Bio-fuels