2 Introduction
The timeline (Fig. 1) for development and understanding of hydrogenase enzymes
covers remarkable progress in the scientific interfaces of micro- and molecular
biology. Beginning nearly a century ago, before isolation of single cells was
common, as well as isolation of enzymes from them, the science of H 2 ase’s has
advanced to the current point where structures of the crystallized giant biomolecules
can be interrogated atom by atom in order to guide understanding of structure and
function. Simultaneous advances in fundamental chemistry [4], especially the
synthesis and isolation of self-assembled iron–sulfur clusters connected their natural inclusion and evolution as electron storage units and electron transport chains.
Special notice must be given to the Cambridge Laboratories and the research of
Stephenson [5, 6], which established fundamental properties of hydrogenases
derived from methanogens nearly a century ago. A historical review of the times
and research of Stephenson is fascinating [7], demonstrating as it does scientific
sleuthing on a practical problem of organic waste degradation and methane production by unidentified microbes in the river Ouse. Despite interruptions from
service in World Wars, her persistence and devotion to bacterial metabolism,
ultimately provided pivotal clues to the properties of the bidirectional hydrogenase
enzymes, and their use in natural methane synthesis by archaea.
According to M. J. Stephenson and her coworker, L. H. Stickland, the microbes
that thrived on the sugar beet waste did not produce alcohol, unlike yeasts, but lived
via an anerobic metabolic pathway that made gases—hydrogen, carbon dioxide,
and the “swamp gas”, methane [4]. She found that their microbial cultures could
chemically reduce methylene blue, in a Thunberg tube, in the presence of hydrogen
but not nitrogen as an alternative. Thus, they established that the microbes contained an enzyme which was widespread, that could activate H 2 , justifying their
appellation of ‘hydrogenase’ [6].
In 1934, Green and Stickland demonstrated the reversibility of the reaction
carried out by hydrogenases [8]. The equilibrium point for the H 2 -induced reduction
of methyl viologen was the same whether colloidal palladium or a bacterial suspension of hydrogenase was used as the catalyst [8]. They quantified their results
over a wide range of H 2 partial pressures and H
+ ion concentrations and found that
the calculated electrochemical potential was identical to that of a standard hydrogen
electrode [8]. Following up on an earlier report [10], Stephenson and Stickland
quantified the bacterial production of hydrogen to formate as 1:1 and formulated the
reaction pathway seen in Fig. 2 [8].
Such results forecast the interest to come of possible technological development
of the enzymes themselves, and the dream of synthetic chemists to develop
molecular catalysts containing cheap first row transition metals as mimetics of
hydrogenase active sites [9].
Such was the beginning of the hydrogenase story; indeed it was only a part of M.
J. Stephenson’s public lecture “How microbes live or some aspects of bacterial
physiology” and her highly regarded publications and treatise, “Bacterial
Organometallic Chemistry Control of Hydrogenases
277
The timeline (Fig. 1) for development and understanding of hydrogenase enzymes
covers remarkable progress in the scientific interfaces of micro- and molecular
biology. Beginning nearly a century ago, before isolation of single cells was
common, as well as isolation of enzymes from them, the science of H 2 ase’s has
advanced to the current point where structures of the crystallized giant biomolecules
can be interrogated atom by atom in order to guide understanding of structure and
function. Simultaneous advances in fundamental chemistry [4], especially the
synthesis and isolation of self-assembled iron–sulfur clusters connected their natural inclusion and evolution as electron storage units and electron transport chains.
Special notice must be given to the Cambridge Laboratories and the research of
Stephenson [5, 6], which established fundamental properties of hydrogenases
derived from methanogens nearly a century ago. A historical review of the times
and research of Stephenson is fascinating [7], demonstrating as it does scientific
sleuthing on a practical problem of organic waste degradation and methane production by unidentified microbes in the river Ouse. Despite interruptions from
service in World Wars, her persistence and devotion to bacterial metabolism,
ultimately provided pivotal clues to the properties of the bidirectional hydrogenase
enzymes, and their use in natural methane synthesis by archaea.
According to M. J. Stephenson and her coworker, L. H. Stickland, the microbes
that thrived on the sugar beet waste did not produce alcohol, unlike yeasts, but lived
via an anerobic metabolic pathway that made gases—hydrogen, carbon dioxide,
and the “swamp gas”, methane [4]. She found that their microbial cultures could
chemically reduce methylene blue, in a Thunberg tube, in the presence of hydrogen
but not nitrogen as an alternative. Thus, they established that the microbes contained an enzyme which was widespread, that could activate H 2 , justifying their
appellation of ‘hydrogenase’ [6].
In 1934, Green and Stickland demonstrated the reversibility of the reaction
carried out by hydrogenases [8]. The equilibrium point for the H 2 -induced reduction
of methyl viologen was the same whether colloidal palladium or a bacterial suspension of hydrogenase was used as the catalyst [8]. They quantified their results
over a wide range of H 2 partial pressures and H
+ ion concentrations and found that
the calculated electrochemical potential was identical to that of a standard hydrogen
electrode [8]. Following up on an earlier report [10], Stephenson and Stickland
quantified the bacterial production of hydrogen to formate as 1:1 and formulated the
reaction pathway seen in Fig. 2 [8].
Such results forecast the interest to come of possible technological development
of the enzymes themselves, and the dream of synthetic chemists to develop
molecular catalysts containing cheap first row transition metals as mimetics of
hydrogenase active sites [9].
Such was the beginning of the hydrogenase story; indeed it was only a part of M.
J. Stephenson’s public lecture “How microbes live or some aspects of bacterial
physiology” and her highly regarded publications and treatise, “Bacterial
Organometallic Chemistry Control of Hydrogenases
277