Abstract
The D-xylose isomerase activity was assayed spectrophotometrically as NADH oxidation in a coupled reaction with the D-arabitol dehydrogenase. The assay system is based on the following reactions:
D-Xylose D-xylose isomerase_??_D-xylulose
D-Xylulose+NADH+H+ D-arabitol dehydrogenase_??_D-arabitol+NAD+
D-Arabitol dehydrogenase was purified from the D-sorbitol-grown cells of Agrobacterium tumefaciens. The standard assay condition is as follows: 5μmoles of Tris-HCl buffer (pH 7, 0), 0.2μmole of MnCl2, 2μl of reduced glutathione (25mg/ml), 0.05μmole of NADH, 6 units of D-arabitol dehydrogenase, 5μmoles of D-xylose and D-xylose isomerase in a total volume of 0.30ml. The reaction was carried out at 30°C. With the assay system, it was confirmed that D-xylose isomerase did not produce D-xylulose from D-lyxose.
