The water-gas shift (WGS) reaction (CO + H2O reversible arrow CO2 + H-2) is of major industrial significance in the production of H, from hydrocarbon sources. High temperatures are required, typically in excess of 200 degrees C, using d-metal catalysts on oxide supports. In our study the WGS process is separated into two half-cell electrochemical reactions (H+ reduction and CO oxidation), catalyzed by enzymes attached to a conducting particle. The H+ reduction reaction is catalyzed by a hydrogenase, Hyd-2, from Escherichia coli, and CO oxidation is catalyzed by a carbon monoxide dehydrogenase (CODH 1) from Carboxydothermus hydrogenoformans. This results in a highly efficient heterogeneous catalyst with a turnover frequency, at 30 degrees C, of at Least 2.5 s(-1) per minimum functional unit (a CODH/Hyd-2 pair) which is comparable to,h-temperature catalysts. conventional high-temperature catalysts.