In vitro hydrogen photoproduction using Pyrococcus furiosus sulfhydrogenase and TiO2

The [NiFe] sulfhydrogenase from the hyperthermophilic archaeon Pyrococcus f uriosus has been tested as a biological catalyst in a light-driven in vitro hydrogen evolution system, using a solar simulator apparatus as a source o f light. The enzyme is active when coupled to photo-induced titanium dioxid e (TiO2) dispersed as submicronic powder in a buffer solution and in the pr esence of the artificial redox mediator methylviologen (MV), carrying elect rons from the TiO2 particle to the enzyme. To optimize the system towards p ractical applications, a simplified version which works in the absence of M V was set up and its performance was assayed with different reductants, as a function of time and over a wide range of temperatures. The comparison of MV-mediated and not-mediated conditions in terms of rate and amount of H-2 photoproduced, highlights a lower efficiency, but an improved overall stab ility of the system when a direct electron transfer from the TiO2 to the en zyme takes place. As a consequence, the reaction lifetime is productively e xtended counteracting the effect of the low H-2 evolution rate with regard to the total amount of Hz photoproduced. In particular, at 60 degrees C the reaction lifetime is prolonged to 8 h, thus resulting in significantly hig her amount of H-2, evolved. The flexibility of the P:furiosus sulfhydrogena se/TiO2 in vitro system with respect to the redox mediator MV and the evide nce that the enzyme performance can be maintained over a wide range of temp eratures (60-80 degrees C) are promising advances in the identification of the optimal conditions for the development of an economically feasible hydr ogen production process exploiting solar light as a source of energy and wa ste compounds as electron donors. (C) 1999 Elsevier Science S.A. All rights reserved.