An alpha-glucuronidase of Schizophyllum commune acting on polymeric xylan

The main alpha-glucuronidase (EC 3.2. 1.131) of the fungus Schizophyllum co mmune was purified to homogeneity using standard chromatographic methods; a nion exchange, hydrophobic interaction chromatography and gel filtration. T he enzyme had a molecular mass of 125 kDa as determined by SDS-polyacrylami de gel electrophoresis and a pI value of 3.6 according to isoelectric focus ing. The N-terminal amino acid sequence of the S. commune alpha-glucuronida se did not show any homology with other alpha-glucuronidases. It exhibited maximal activity at pH values from 4.5 to 5.5 and was stable for 24 h betwe en pH 6 and 8 at 40 degrees C. The highest temperature at which the enzyme retained its full activity for 24 h at pH 5.8 was 40 degrees C. The alpha-g lucuronidase of S.commune was able to remove almost all 4-O-methylglucuroni c acid groups from water-soluble polymeric softwood arabinoglucuronoxylans. The action of the enzyme on birchwood acetyl-glucuronoxylan was limited du e to the high amount of acetyl substituents. The degree of hydrolysis of pa rtially soluble deacetylated glucuronoxylan did not exceed 50% of the theor etical maximum. However, together with a xylanase hydrolysing the xylan bac kbone the action of the alpha-glucuronidase of S. commune on glucuronoxylan was clearly enhanced. It was apparent that the enzyme was able to remove t he 4-O-methylglucuronic groups mainly from soluble substrates. (C) 2000 Els evier Science B.V. All rights reserved.