초록
<P/><P>The <SMALL>L</SMALL>-arabinose isomerase (<SMALL>L</SMALL>-AI) and the <SMALL>D</SMALL>-xylose isomerase (<SMALL>D</SMALL>-XI) encoding genes from <I>Lactobacillus reuteri</I> (DSMZ 17509) were cloned and overexpressed in <I>Escherichia coli</I> BL21 (DE3). The proteins were purified to homogeneity by one-step affinity chromatography and characterized biochemically. <SMALL>L</SMALL>-AI displayed maximum activity at 65 °C and pH 6.0, whereas <SMALL>D</SMALL>-XI showed maximum activity at 65 °C and pH 5.0. Both enzymes require divalent metal ions. The genes were also ligated into the inducible lactobacillal expression vectors pSIP409 and pSIP609, the latter containing a food grade auxotrophy marker instead of an antibiotic resistance marker, and the <SMALL>L</SMALL>-AI- and <SMALL>D</SMALL>-XI-encoding sequences/genes were coexpressed in the food grade host <I>Lactobacillus plantarum</I>. The recombinant enzymes were tested for applications in carbohydrate conversion reactions of industrial relevance. The purified <SMALL>L</SMALL>-AI converted <SMALL>D</SMALL>-galactose to <SMALL>D</SMALL>-tagatose with a maximum conversion rate of 35%, and the <SMALL>D</SMALL>-XI isomerized <SMALL>D</SMALL>-glucose to <SMALL>D</SMALL>-fructose with a maximum conversion rate of 48% at 60 °C.</P>