Enzyme chemistry hydrogenase

Nickel is found in thiolate/sulflde environment in the [NiFe]-hydrogenases and in CODH/ACS.33 In addition, either a mononuclear Ni-thiolate site or a dinuclear cysteine-S bridged structure are assumed plausible for the new class of Ni-containing superoxide dismutases, NiSOD (A).34 [NiFe]-hydrogenase catalyzes the two-electron redox chemistry of dihydrogen. Several crystal structures of [NiFe]-hydrogenases have demonstrated that the active site of the enzyme consists of a heterodinuclear Ni—Fe unit bound to thiolate sulfurs of cysteine residues with a Ni—Fe distance below 3 A (4) 35-39 This heterodinuclear active site has been the target of extensive model studies, which are summarized in Section 6.3.4.12.5. 

In view of its application to fuel cell development, research into hydrogen activation remains a forefront area for chemists, physicists, and biologists (7). A rekindling of opportunity and excitement in this field of chemistry has come from the delineation of simple catalytic sites of hydrogenase enzymes as displayed by protein crystal structures published within the last decade (2 10). These active sites hold out promise of using complexes comprised of base metals such as iron or... 

A potentially promising route to learn more about the complex redox chemistry of hydrogenase is to look at the direct electron transfer between the enzyme and an electrode. A study of this phenomenon may also be relevant to a possible coupling of solar cells with hydrogenasecatalyzed H2 production. Results from this line of research have thus far been very limited. A response was obtained in differential-pulse polarography on the dropping mercury electrode modified with polylysine (cf. van Dijk et al., 1985). Attempts to use... 

Lubitz W, Ogata H, Reijerse E, Higuchi Y. Structure and function of hydrogenase enzymes. In Wydrzynski TJ, Hillier W, editors. Molecular solar fuels. Cambridge, UK The Royal Society of Chemistry 2012. p. 288-325. 

The chemistry of model systems of hydrogenase enzymes has developed along with the study of the enzymes. Developments in the characterization of the enzyme have spurred the development of model systems that provide a better understanding of the function of the enzyme. Ultimately, a complete understanding of the chemistry of the hydrogenase enzymes will require the synthesis of both areas of study. In this review we consider the work that has been done to characterize the enzyme, focussing on the areas that are amenable for study using model systems. We then... 

Many spectroscopic models have focussed on reproducing the unusual EPR properties of the different paramagnetic states of the active sites of the hydrogenase enzymes. Model chemistry should be instrumental in determining the coordination geometry and oxidation state of the paramagnetic center. As we mentioned above, the nickel ion has been implicated as the source of the EPR signals of the active site and model ehemistry has focussed on monomeric nickel complexes. 

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