Occurrence, classification, and biological function of hydrogenases: An overview

The phylogenetic analyses of the biological function of hydrogenases have led to the identification of several phylogenetically distinct groups and subgroups that form the basis of coherent system of classification. Hydrgeneses are a structurally and functionally diverse group of enzymes and efforts have been made to augment them. This showed the presence of such enzymes in a variety of organisms including pathogens and of multiple hydrogenases. The roles of such enzymes and their biosynthesis and activity can be derived from its postgenomic analysis. Hydrogenases' main role is the oxidation of H2 or the reduction of protons, coupled to energy-conserving electron-transfer chain reactions. This permits energy to be obtained from H2 or from the oxidation of substrates of lower potential. They are restricted to the prokaryotes but nevertheless widely distributed. The biological production of H2 has been stimulated by interests in finding alternatives in fossil fuels. Structural studies of hydrogenases will be relevant in directing protein engineering. Also of relevance is the investigation of H2 metabolism and regulation for engineering microorganisms at the cellular level to maximize H2 production. Many of the so-far uncultivated species will then contain hydrogenases.