PURIFICATION AND CHARACTERIZATION OF THE ALPHA-GLUCURONIDASE FROM THERMOANAEROBACTERIUM SP. STRAIN JW/SL-YS485, AN IMPORTANT ENZYME FOR THE UTILIZATION OF SUBSTITUTED XYLANS

A cell-associated alpha-glucuronidase was purified to gel electrophoretic homogeneity from the thermophilic anaerobic bacterium Thermoanaerobacterium sp, strain JW/SL-YS485. This enzyme had a pI of 4.65, a molecular weight of 130,000, and two subunits; the molecular weight of each subunit was 74,000. The enzyme exhibited the highest level of activity at pH 5.4 and 60 degrees C, as determined by a 5-min assay. The K-m and k(cat) values of the enzyme for 4-methylglucuronosyl xylobiose were 0.76 mM and 1,083 IU/mu mol, respectively. The Arrhenius energy was 26.4 kJ/mol. The specific activities of the enzyme with 4-O-methylglucuronosyl xylobiose, 4-O-methylglucuronosyl xylotriose, and 4-O-methylglucuronosyl xylotetraose were 8.4, 4.8, and 3.9 IU/mg, respectively. The purified alpha-glucuronidase and a beta-xylosidase purified from the same organism interacted synergistically to hydrolyze 4-methylglucuronosyl xylotetraose.