Characterization of an Agrobacterium tumefaciensd-Psicose 3-Epimerase That Converts d-Fructose to d-Psicose

다국어 초록 (Multilingual Abstract)

<B>ABSTRACT</B><P>The noncharacterized gene previously proposed as the d-tagatose 3-epimerase gene from <I>Agrobacterium tumefaciens</I> was cloned and expressed in <I>Escherichia coli</I>. The expressed enzyme was purified by three-step chromatography with a final specific activity of 8.89 U/mg. The molecular mass of the purified protein was estimated to be 132 kDa of four identical subunits. Mn<SUP>2+</SUP> significantly increased the epimerization rate from d-fructose to d-psicose. The enzyme exhibited maximal activity at 50°C and pH 8.0 with Mn<SUP>2+</SUP>. The turnover number (<I>k</I>cat) and catalytic efficiency (<I>k</I>cat/<I>Km</I>) of the enzyme for d-psicose were markedly higher than those for d-tagatose, suggesting that the enzyme is not d-tagatose 3-epimerase but d-psicose 3-epimerase. The equilibrium ratio between d-psicose and d-fructose was 32:68 at 30°C. d-Psicose was produced at 230 g/liter from 700-g/liter d-fructose at 50°C after 100 min, corresponding to a conversion yield of 32.9%.</P>