Isolation and Characterization of a Soluble NADPH-Dependent Fe(III) Reductase from Geobacter sulfurreducens

In this study we describe the purification and characterization of an enzyme from G. sulfurreducens that catalyzes the reduction of soluble Fe(III) with NADPH as the electron donor

Franz Kaufmann

2002

Scholarcy highlights

  • Dissimilatory Fe(III) reduction plays an important role in the degradation of natural and contaminant organic matter under anaerobic conditions
  • NADPH is an intermediate in the oxidation of organic compounds coupled to Fe(III) reduction in Geobacter species, but Fe(III) reduction with NADPH as the electron donor has not been studied in these organisms
  • The genes encoding the two subunits were identified in the complete sequence of the G. sulfurreducens genome from the N-terminal amino acid sequences derived from the subunits of the purified protein
  • G. sulfurreducens strain PCA was obtained from our laboratory culture collection and cultivated in an anaerobic freshwater medium, containing 20 mM sodium acetate as the electron donor and either 50 mM ferric citrate or 40 mM fumarate as the electron acceptor, under an atmosphere of N2-CO2
  • A similar distribution was found for malate dehydrogenase, an enzyme known to reside in the cytoplasm
  • Fe(III) complexed with EDTA or citrate was reduced at rates less than 5% of that observed with Fe(III)-nitrilotriacetic acid
  • Cytochromes have been considered to be important electron carriers associated with these membrane-bound Fe(III) reductase activities
  • The purified soluble Fe(III) reductase possessed high methyl viologen:NADPϩ oxidoreductase activity, and it could be hypothesized that the enzyme is involved in transferring electrons from reduced ferredoxin to NADPϩ

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