Novel substrate specificity of D-arabinose isomerase from Klebsiella pneumoniae and its application to production of D-altrose from D-psicose.

d -Arabinose isomerase from Klebsiella pneumoniae 40bXX was purified 12-fold with a 62.5% yield indicated by its electrophoretic homogeneity. The purified enzyme showed the highest activities toward d -arabinose and l -fucose as substrates at optimum conditions (50 mM glycine–NaOH, pH 9.0, 40°C). The enzyme had a broad range of substrate specificities toward various d / l -aldoses, i.e. , d -arabinose, l -fucose, d / l -xylose, d -mannose, d / l -lyxose, l -glucose, d -altrose and d / l -galactose. The equilibrium ratios between d -arabinose and d -ribulose, l -fucose and l -fuculose, d -altrose and d -psicose, and l -galactose and l -tagatose were 90:10, 90:10, 13:87 and 25:75, respectively. Using a combination of the immobilized d -tagatose 3-epimerase and d -arabinose isomerase, we achieved the production of d -altrose from d -fructose in a batch reactor. We successfully produced approximately 12 g of d -altrose from 200 g of d -fructose in a reaction series with an overall yield of 6%. The product obtained was confirmed to be d -altrose by HPLC and 13 C-NMR. To the best of our knowledge, this is the first report on the production of d -altrose from a cheap sugar, d -fructose, using an enzymatic method.