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J. Bacteriol., 08 1995, 4757-4764, Vol 177, No. 16
J Heider, K Ma and MW Adams
Thermococcus strain ES-1 is a strictly anaerobic, hyperthermophilic
archaeon that grows at temperatures up to 91 degrees C by the fermentation
of peptides. It is obligately dependent upon elemental sulfur (S(o)) for
growth, which it reduces to H2S. Cell extracts contain high aldehyde
oxidation activity with viologen dyes as electron acceptors. The enzyme
responsible, which we term aldehyde ferredoxin oxidoreductase (AOR), has
been purified to electrophoretic homogeneity. AOR is a homodimeric protein
with a subunit M(r) of approximately 67,000. It contains molybdopterin and
one W, four to five Fe, one Mg, and two P atoms per subunit. Electron
paramagnetic resonance analyses of the reduced enzyme indicated the
presence of a single [4Fe-4S]+ cluster with an S = 3/2 ground state. While
AOR oxidized a wide range of aliphatic and aromatic aldehydes, those with
the highest apparent kcat/Km values (> 10 microM-1S-1) were
acetaldehyde, isovalerylaldehyde, and phenylacetaldehyde (Km values of <
100 microM). The apparent Km value for Thermococcus strain ES-1 ferredoxin
was 10 microM (with crotonaldehyde as the substrate). Thermococcus strain
ES-1 AOR also catalyzed the reduction of acetate (apparent Km of 1.8 mM)
below pH 6.0 (with reduced methyl viologen as the electron donor) but at
much less than 1% of the rate of the oxidative reaction (with benzyl
viologen as the electron acceptor at pH 6.0 to 10.0).(ABSTRACT TRUNCATED AT
250 WORDS)
Copyright © 1995, American Society for Microbiology
Purification, characterization, and metabolic function of tungsten- containing aldehyde ferredoxin oxidoreductase from the hyperthermophilic and proteolytic archaeon Thermococcus strain ES-1
Department of Biochemistry and Molecular Biology, University of Georgia, Athens 30602, USA.
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