期刊
JOURNAL OF BACTERIOLOGY
卷 193, 期 12, 页码 3009-3019出版社
AMER SOC MICROBIOLOGY
DOI: 10.1128/JB.01433-10
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资金
- Natural Sciences and Engineering Research Council (Canada)
- Canada Foundation for Innovation
An alcohol dehydrogenase (ADH) from hyperthermophilic archaeon Thermococcus guaymasensis was purified to homogeneity and was found to be a homotetramer with a subunit size of 40 +/- 1 kDa. The gene encoding the enzyme was cloned and sequenced; this gene had 1,095 bp, corresponding to 365 amino acids, and showed high sequence homology to zinc-containing ADHs and L-threonine dehydrogenases with binding motifs of catalytic zinc and NADP(+). Metal analyses revealed that this NADP(+) -dependent enzyme contained 0.9 +/- 0.03 g-atoms of zinc per subunit. It was a primary-secondary ADH and exhibited a substrate preference for secondary alcohols and corresponding ketones. Particularly, the enzyme with unusual stereoselectivity catalyzed an anti-Prelog reduction of racemic (R/S)-acetoin to (2R, 3R)-2,3-butanediol and meso-2,3-butanediol. The optimal pH values for the oxidation and formation of alcohols were 10.5 and 7.5, respectively. Besides being hyper-thermostable, the enzyme activity increased as the temperature was elevated up to 95 degrees C. The enzyme was active in the presence of methanol up to 40% (vol/vol) in the assay mixture. The reduction of ketones underwent high efficiency by coupling with excess isopropanol to regenerate NADPH. The kinetic parameters of the enzyme showed that the apparent K-m values and catalytic efficiency for NADPH were 40 times lower and 5 times higher than those for NADP(+), respectively. The physiological roles of the enzyme were proposed to be in the formation of alcohols such as ethanol or acetoin concomitant to the NADPH oxidation.
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