Af. Arendsen et al., REDOX CHEMISTRY OF BIOLOGICAL TUNGSTEN - AN EPR STUDY OF THE ALDEHYDEOXIDOREDUCTASE FROM PYROCOCCUS-FURIOSUS, JBIC. Journal of biological inorganic chemistry, 1(4), 1996, pp. 292-296
Aldehyde:ferredoxin oxidoreductase (AOR) from the hyperthermophilic ar
chaeon Pyrococcus furiosus is a homodimeric protein. Each subunit carr
ies one [4Fe-4S] cubane and a novel tungsten cofactor containing two p
terins. A single iron atom bridges between the subunits. AOR has previ
ously been studied with EPR spectroscopy in an inactive form known as
the red tungsten protein (RTP): reduced RTP exhibits complex EPR inter
action signals. We have now investigated the active enzyme AOR with EP
R, and we have found an S = 1/2 plus S = 3/2 spin mixture from a non-i
nteracting [4Fe-4S](1+) cluster in the reduced enzyme. Oxidized AOR af
fords EPR signals typical for W(V) with g-values of 1.982, 1.953, and
1.885. The W(V) signals disappear at a reduction potential E(m,7.5) of
+ 180 mV. This unexpectedly high value indicates that the active-site
redox chemistry is based on the pterin part of the cofactor.