Abstract
A new α-glucuronidase that specifically hydrolyzed O-α-D-glucosyluronic acid α-D-glucosiduronic acid (trehalose dicarboxylate, TreDC) was purified from a commercial enzyme preparation from Aspergillus niger, and its properties were examined. The enzyme did not degrade O-α-D-glucosyluronic acid α-D-glucoside, O-α-D-glucosyluronic acid β-D-glucosiduronic acid, O-α-D-glucosyluronic acid-(1→2)-β-D-fructosiduronic acid, p-nitrophenyl-O-α-D-glucosiduronic acid, methyl-O-α-D-glucosiduronic acid, or 6-O-α-(4-O-α-D-glucosyluronic acid)-D-glucosyl-β-cyclodextrine. Furthermore, it showed no activity on α-glucuronyl linkages of 4-O-methyl-D-glucosyluronic acid-α-(1→2)-xylooligosaccharides, derived from xylan, a supposed substrate of α-glucuronidases.
The molecular mass of the enzyme was estimated to be 120 kDa by gel filtration and 58 kDa by SDS–PAGE suggesting, the enzyme is composed of two identical subunits. It was most active at pH 3.0–3.5 and at 40 °C. It was stable in pH 2.0–4.5 and below 30 °C. It hydrolyzed O-α-D-glucosyluronic acid α-D-glucosiduronic acid to produce α- and β-anomers of D-glucuronic acid in an equimolar ratio. This result suggests that inversion of the anomeric configuration of the substrate is involved in the hydrolysis mechanism.
