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Journal of Bacteriology, February 1999, p. 1163-1170, Vol. 181, No. 4
Department of Biochemistry and Molecular
Biology and Center for Metalloenzyme Studies, University of
Georgia, Athens, Georgia 30602
Received 9 July 1998/Accepted 30 November 1998
Pyrococcus furiosus is a hyperthermophilic archaeon
that grows optimally at 100°C by the fermentation of peptides and
carbohydrates to produce acetate, CO2, and H2,
together with minor amounts of ethanol. The organism also generates
H2S in the presence of elemental sulfur (S0).
Cell extracts contained NADP-dependent alcohol dehydrogenase activity
(0.2 to 0.5 U/mg) with ethanol as the substrate, the specific activity
of which was comparable in cells grown with and without S0.
The enzyme was purified by multistep column chromatography. It has a
subunit molecular weight of 48,000 ± 1,000, appears to be a
homohexamer, and contains iron (~1.0 g-atom/subunit) and zinc (~1.0
g-atom/subunit) as determined by chemical analysis and plasma emission
spectroscopy. Neither other metals nor acid-labile sulfur was detected.
Analysis using electron paramagnetic resonance spectroscopy indicated
that the iron was present as low-spin Fe(II). The enzyme is oxygen
sensitive and has a half-life in air of about 1 h at 23°C. It is
stable under anaerobic conditions even at high temperature, with
half-lives at 85 and 95°C of 160 and 7 h, respectively. The
optimum pH for ethanol oxidation was between 9.4 and 10.2 (at 80°C),
and the apparent Kms (at 80°C) for ethanol,
acetaldehyde, NADP, and NAD were 29.4, 0.17, 0.071, and 20 mM,
respectively. P. furiosus alcohol dehydrogenase utilizes a
range of alcohols and aldehydes, including ethanol, 2-phenylethanol,
tryptophol, 1,3-propanediol, acetaldehyde, phenylacetaldehyde, and
methyl glyoxal. Kinetic analyses indicated a marked preference for
catalyzing aldehyde reduction with NADPH as the electron donor.
Accordingly, the proposed physiological role of this unusual alcohol
dehydrogenase is in the production of alcohols. This reaction
simultaneously disposes of excess reducing equivalents and removes
toxic aldehydes, both of which are products of fermentation.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
An Unusual Oxygen-Sensitive, Iron- and
Zinc-Containing Alcohol Dehydrogenase from the Hyperthermophilic
Archaeon Pyrococcus furiosus
*
Corresponding author. Mailing address: Department of
Biochemistry, Life Sciences Building, University of Georgia, Athens, GA
30602. Phone: (706) 542-2060. Fax: (706) 542-0229. E-mail: adams{at}bmb.uga.edu.
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