Abstract
Aldehyde:ferredoxin oxidoreductase (AOR) from the hyperthermophilic archaeon Pyrococcus fu- riosus is a homodimeric protein. Each subunit carries one (4Fe-4S) cubane and a novel tungsten cofactor con- taining two pterins. A single iron atom bridges between the subunits. AOR has previously been studied with EPR spectroscopy in an inactive form known as the red tungsten protein (RTP): reduced RTP exhibits complex EPR interaction signals. We have now investigated the active enzyme AOR with EPR, and we have found an S p 1/2 plus S p 3/2 spin mixture from a non-interact- ing (4Fe-4S) 1c cluster in the reduced enzyme. Oxidized AOR affords EPR signals typical for W(V) with g-val- ues of 1.982, 1.953, and 1.885. The W(V) signals disap- pear at a reduction potential Em,7.5 of c180 mV. This unexpectedly high value indicates that the active-site redox chemistry is based on the pterin part of the cofac- tor.
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