Hydrogenases Biorganometallic Formation and Splitting of Dihydrogen

The study of H-ases is a very active, vast research field ( 3000 publications) that has been the subject of many reviews.2 11 Only the aspects directly involving the biological activation and production of H2 will be discussed here. Most notably, the active sites of H-ases feature the first biological systems with CO and cyanide ligands. These are coordinated to dinuclear M-M bonded centers, such as shown in 1 

H-ases are redox enzymes that catalyze reversible interconversion of H2 and protons to either utilize H2 as an energy source or dispose excess electrons as H2  

Equation (10.1) is a rare true equilibrium process much like the hydrogen electrode e.g., there is dependence on the H2 pressure whether H2 is produced or consumed. From isotope exchange evidence (such as the catalytic reaction shown in Eq. (10.2) wherein the HD/H2 ratio is pH-dependent), it is inferred that the H2 molecule is spht heterolytically. 

The enzymes are crucial to hydrogen metabolism, which is essential to microorgan- 

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