Hydrogenases metal-free enzyme

As discussed previously, superelectrophilic activation in biological systems has been found even with a metal-free hydrogenase enzyme found in methanogenic archea, an enzymatic system that converts CO2 to methane.57 It was found that /V5./V10-menthyl tetrahydromethanopterin (42) undergoes an enzyme-catalyzed reaction with H2 by hydride transfer to the pro-R position and release of a proton to form the reduced product (43 eq 36). 

As described in Chapter 2, a unique gitonic superelectrophile is considered to be involved in an enzyme system that converts CO2 to methane. Berkessel and Thauer have studied this metal-free hydrogenase enzyme from methanogenic archaea and a mechanism is proposed involving activation through a vicinal-superelectrophilic system (eq 34).50... 

The metal-free hydrogenase enzyme system was also studied by theoretical calculations.52 This study involved the reactions of two model systems (115 and 116) with molecular hydrogen (Table 3). Cation 115... 

Lyon EJ, Shima S, Buurman G, Chowdhuri S, Batschauer A, Steinbach K, Thauer RK (2004) UV-A/blue-light inactivation of the metal-free hydrogenase (Hmd) from methanogenic archaea. The enzyme contains functional iron after all. Eur. J. Biochem. 271 195-204... 

Ge2-alkyne analogs to give a mixture of Gc2 and primary germane products (Scheme 11.4) has been described by Power and coworkers [23]. It is also noteworthy that a unique metal-free hydrogenase has been identified from methanogenic archaea. This enzyme catalyzes reactions with H2 [24, 25], and it is suggested that a folate-Hke cofactor is important in the the reversible activation or liberation of H2 [26, 27]. 

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