Biohydrogen: Chapter 5. Hydrogenase

Several evolutionary models proposed that molecular hydrogen (H2) was the primary energy source on the early Earth, exerting a major influence on the origin of life. Hydrogenase, the enzyme catalyzing the interconversion of H2 into protons and electrons, is thus considered an ancestral invention, for which the molecular structure and architecture have been thoroughly adapted for specialized tasks, undertaken in peculiar environments, during the course of the evolution. Three different types of hydrogenase can be distinguished on the basis of the metal content of their active site, namely, [NiFe]-hydrogenase, [FeFe]-hydrogenase, and [Fe]-hydrogenase. Although they share common features, taxonomic distribution, maturation apparatus, and physiological role differ substantially among the three different classes of hydrogenases. These metalloenzymes are thus considered a classical example of convergent evolution. The notion that “there is much to learn from nature” holds great promise for biohydrogen applications, and this has been demonstrated by the emergence of bioengineering strategies used to design synthetic metabolic pathways and improve the O2 tolerance of hydrogenases. This chapter provides an overview of the diversity and physiological role of hydrogenases, with a particular emphasis on their biotechnological potential.