초록
<P><B>ABSTRACT</B><P> Enzymatic processes are useful for industrially important sugar production, and <I>in vitro</I> two-step isomerization has proven to be an efficient process in utilizing readily available sugar sources. A hypothetical uncharacterized protein encoded by <I>ydaE</I> of Bacillus licheniformis was found to have broad substrate specificities and has shown high catalytic efficiency on d -lyxose, suggesting that the enzyme is d -lyxose isomerase. Escherichia coli BL21 expressing the recombinant protein, of 19.5 kDa, showed higher activity at 40 to 45°C and pH 7.5 to 8.0 in the presence of 1.0 mM Mn <SUP>2+</SUP> . The apparent <I> K m</I> values for d -lyxose and d -mannose were 30.4 ± 0.7 mM and 26 ± 0.8 mM, respectively. The catalytic efficiency ( <I>k</I>cat / <I> K m</I> ) for lyxose (3.2 ± 0.1 mM <SUP>−1</SUP> s <SUP>−1</SUP> ) was higher than that for d -mannose (1.6 mM <SUP>−1</SUP> s <SUP>−1</SUP> ). The purified protein was applied to the bioproduction of d -lyxose and d -glucose from d -xylose and d -mannose, respectively, along with the thermostable xylose isomerase of Thermus thermophilus HB08. From an initial concentration of 10 mM d -lyxose and d -mannose, 3.7 mM and 3.8 mM d -lyxose and d -glucose, respectively, were produced by two-step isomerization. This two-step isomerization is an easy method for <I>in vitro</I> catalysis and can be applied to industrial production. </P></P>