P.K. Widman J.C. Woodward Elizabeth J.P. Phillips Derek R. Lovley 1993 <p>The mechanism for U(VI) reduction by <i>Desulfovibrio vulgaris</i> (Hildenborough) was investigated. The H₂-dependent U(VI) reductase activity in the soluble fraction of the cells was lost when the soluble fraction was passed over a cationic exchange column which extracted cytochrome <i>c</i>₃. Addition of cytochrome <i>c</i>₃ back to the soluble fraction that had been passed over the cationic exchange column restored the U(VI)-reducing capacity. Reduced cytochrome <i>c</i>₃ was oxidized by U(VI), as was a <i>c</i>-type cytochrome(s) in whole-cell suspensions. When cytochrome <i>c</i>₃ was combined with hydrogenase, its physiological electron donor, U(VI) was reduced in the presence of H₂. Hydrogenase alone could not reduce U(VI). Rapid U(VI) reduction was followed by a subsequent slow precipitation of the U(IV) mineral uraninite. Cytochrome <i>c</i>₃ reduced U(VI) in a uranium-contaminated surface water and groundwater. Cytochrome <i>c</i>₃ provides the first enzyme model for the reduction and biomineralization of uranium in sedimentary environments. Furthermore, the finding that cytochrome <i>c</i>₃ can catalyze the reductive precipitation of uranium may aid in the development of fixed-enzyme reactors and/or organisms with enhanced U(VI)-reducing capacity for the bioremediation of uranium- contaminated waters and waste streams.</p> application/pdf 10.1128/aem.59.11.3572-3576.1993 en American Society for Microbiology Reduction of uranium by cytochrome c3 of Desulfovibrio vulgaris article