Purification and characterization of a β-glucuronidase from Aspergillus niger

A P-glucuronidase from Pectinex Ultra SP-L, a commercial pectolytic enzyme preparation from Aspergillus niger, was purified 170-fold by ion-exchange chromatography and gel filtration. Apparent M-r of the purified enzyme, estimated by denaturing gel electrophoresis and size-exclusion chromatography, were 68,000 and 71,000, respectively, indicating that the enzyme is a monomeric protein. It released uronic acids not only from p-nitrophenyl beta -glucosiduronic acid (PNP-GlcA) but also from acidic galactooligosaccharides carrying either beta -D-glucosyluronic or 4-O-methyl-beta -D-glucosyluronic residues at the nonreducing termini through beta-(1 --> 6)-glycosidic linkags. The enzyme exhibited a maximal activity toward these substrates at pH 3.0. A regioisomer, 3-O-beta -glucosyluronic acid-galactose, was unsusceptible to the enzyme. The enzyme did act on a polymer substrate, releasing uronic acid from the carbohydrate portion of a radish arabinogalactan - protein modified by treatment with fungal alpha -L-arabinofuranosidase. The enzyme produced acidic oligosaccharides by transglycosplation, catalyzing the transfer of uronic acid residues of PNP-GlcA and 6-O-beta -glucosyluronic acid-galactose to certain exogenous acceptor sugars such as Gal, N-acetylgalactosamine, Glc, and xylose. (C) 2001 Elsevier Science Ltd. All rights reserved.