Di-iron hydrogenase (Fe-Fe hydrogenase) is a bacterial enzyme that helps the bacteria to produce hydrogen from water. Some bacterial enzymes have a huge turnover of 10^4/s for the production of hydrogen from water. (Selloni et. al. 2013).
Researchers have found that the efficient catalytic site in the isolated [FeFe] H subcluster is the Fe d center distal (d) to the [4Fe-4S] H cluster while the other iron site, i.e. the proximal Fe p, has higher energy barriers. (Sbraccia et. al.)
It is one of the inspirational natural materials for scientists to produce hydrogen for its utilization as a fuel.
P. H.- L. Sit, R. Car, M. H. Cohen, A. Selloni, 2013. Oxygen tolerance of an in silico-designed bioinspired hydrogen-evolving catalyst in water. Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1215149110
Sbraccia C, Zipoli F, Car R, Cohen MH, Dismukes GC, Selloni A., (2008). Mechanism of H2 production by the [FeFe]H subcluster of di-iron hydrogenases: implications for abiotic catalysts. The journal of Physical Chemistry. B. doi: 10.1021/jp803657b