Biological Formation of Molecular Hydrogen

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Science  09 Apr 1965:
Vol. 148, Issue 3667, pp. 186-192
DOI: 10.1126/science.148.3667.186


From a general standpoint, the formation of molecular hydrogen can be considered a device for disposal of electrons released in metabolic oxidations. We presume that this means of performing anaerobic oxidations is of ancient origin and that the hydrogen-evolving system of strict anaerobes represents a primitive form of cytochrome oxidase, which in aerobes effects the terminal step of respiration, namely the disposal of electrons by combination with molecular oxygen. We further assume that the original pattern of reactions leading to H2 production has become modified in various ways (with respect to both mechanisms and functions) during the course of biochemical evolution, and we believe that this point of view suggests profitable approaches for clarifying a number of problems in the intermediary metabolism of microorganisms which produce or utilize H2. Of special general importance in this connection is the basic problem of defining more precisely the fundamental elements in the regulatory control of anaerobic energy metabolism. Among the more specific aspects awaiting further elucidation are: the relations between formation of H2 and use of H2 as a primary reductant for biosynthetic purposes; the various forms of direct and indirect interactions between hydrogenase and N2 reduction systems; and the transitional stages between anaerobic and aerobic energy-metabolism patterns of facultative organisms.