by PhilipJ on 6 March 2009
Hydrogen gas is an unusual substance. Normally, it is stable and must be coaxed with powerful catalysts to enter into chemical reactions. But when mixed with oxygen, a tiny spark will set off an explosive chain reaction. Hydrogen gas holds great promise to be the greenest of green energy sources. It has many advantages: compared with many fuels, it releases a lot of energy for its weight, and the reaction forms only energy and pure water. It has substantial disadvantages, however. It is dangerous to store, and it is difficult to perform the reaction in a controlled, non-explosive manner. Currently, the fuel cells being developed for use in hydrogen-powered vehicles use costly platinum catalysts to perform this reaction. Researchers are now looking to nature for other alternatives.
Enzymes that split hydrogen gas have evolved at least three separate times in the history of life on the Earth. These enzymes are used either to split hydrogen gas for use as energy, or to create hydrogen gas as a product of their reaction. Three examples are shown here. At the top is a nickel-iron hydrogenase (PDB entry 2frv), in the center is an iron-iron hydrogenase (PDB entry 1feh), and at the bottom is an iron hydrogenase (PDB entry 3dag and 3f47). As the names imply, all of them use metal ions in their reactions.
Read the rest by David Goodsell at the RCSB PDB