The importance of hydrogen to biological systems is emphasized by its central position in
table. Hydrogen is a constituent of water and nearly all organic molecules. Cells
use H+ gradients to drive ATP synthesis, solute transport, and flagella rotation.
Hydrogenase enzymes (reviewed by Vignais et al, 2001) mediate the redox interconversion of H+ and
H2. Some aerobic
(Friedrich and Schwarz, 1993) and anaerobic
(Gross and Simon, 2003) chemolithotrophic prokaryotes can derive energy for
growth from the oxidation of H2, catalyzed by [NiFe]-hydrogenases. [Fe]-Hydrogenases
typically associated with the reduction of H+ leading to the evolution of
H2 (Frey, 2002), and are found in both prokaryotes
(Nandi and Sengupta, 1998) and lower eukaryotes (some fungi, algae, and protozoa)
(Horner et al, 2002).
Metal-free hydrogenases have been discovered in methanogenic archaea
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