초록
<P>A novel thermostable alcohol dehydrogenase (ADH) showing activity toward aromatic secondary alcohols was identified from the hyperthermophilic archaeon <I>Thermococcus kodakarensis</I> KOD1 (<I>Tk</I>ADH). The gene, <I>tk0845</I>, which encodes an aldo-keto reductase, was heterologously expressed in <I>Escherichia coli</I>. The enzyme was found to be a monomer with a molecular mass of 31 kDa. It was highly thermostable with an optimal temperature of 90°C and a half-life of 4.5 h at 95°C. The apparent <I>K<SUB>m</SUB></I> values for the cofactors NAD(P)<SUP>+</SUP> and NADPH were similar within a range of 66 to 127 μM. <I>Tk</I>ADH preferred secondary alcohols and accepted various ketones and aldehydes as substrates. Interestingly, the enzyme could oxidize 1-phenylethanol and its derivatives having substituents at the <I>meta</I> and <I>para</I> positions with high enantioselectivity, yielding the corresponding (<I>R</I>)-alcohols with optical purities of greater than 99.8% enantiomeric excess (ee). <I>Tk</I>ADH could also reduce 2,2,2-trifluoroacetophenone to (<I>R</I>)-2,2,2-trifluoro-1-phenylethanol with high enantioselectivity (>99.6% ee). Furthermore, the enzyme showed high resistance to organic solvents and was particularly highly active in the presence of H<SUB>2</SUB>O–20% 2-propanol and H<SUB>2</SUB>O–50% <I>n</I>-hexane or <I>n</I>-octane. This ADH is expected to be a useful tool for the production of aromatic chiral alcohols.</P>