Characterization of hydrogenase activities associated with the molybdenum CO dehydrogenase from Oligotropha carboxidovorans

The formation of H-2 by chemolithoautrophically growing Oligotropha carboxidovorans has been identified as the result of the oxidation of CO mediated by the cytoplasmic species of the molybdenum-containing CO dehydrogenase multienzyme complex as follows: CO + H2O --> CO2 + H-2. Purified CO dehydrogenase was shown to carry hydrogen uptake and formation activities in addition to its catabolic function which is the oxidation of CO. Among the electron donors supporting H-2 formation were CO, NADH, reduced flavins and reduced viologen dyes. The reduction of protons to H-2 by cytoplasmic CO dehydrogenase is interpreted as a detoxification reaction for electrons to prevent cell damage in O. carboxidovorans.