β-glucosidase components of the cellulolytic system of the edible straw mushroom, Volvariella volvacea

The edible straw mushroom, Volvariella volvacea (V-14), produced beta-glucosidase when grown in liquid culture on a variety of carbon sources including cellulose, cellobiose, salicin, sorbose, lactose, esculin, cotton wool, and filter paper. Two cell-associated beta-glucosidases, BGL-I and BGL-II, were purified 32-fold and 23-fold, respectively, from extracts of cellulose-grown mycelium. The purification procedure included DEAE-Sepharose chromatography, Sephacryl S-200 chromatography, and fast protein liquid chromatography (FPLC) using Mono-e and Mono-P anion-exchange columns: The enzymes were found to be homogeneous and to have native molecular weights of 158 kDa (BGL-I) and 256 kDa (BGL-II) by gelfiltration. The isoelectric points for BGL-I and BGL-II were 5.6 and 5-5.2, respectively. Both isozymes displayed relatively broad pH optima with maximum reaction velocities recorded at pH 7.0 for BGL-I and pH 6.2 for BGL-II, and were rapidly denatured at temperatures of 60 degrees C and above. Purified BGL-I and BGL-II were both active against p-nitrophenyl-beta-D-glucopyranoside, p-nitrophenyl-alpha-L-arabinofuranoside, p-nitrophenyl-alpha-D-glucopyranoside, cellobiose, salicin, and esculin, but only BGL-I was active against p-nitrophenyl-beta-D-xylopyranoside. BGL-I and BGL-II exhibited K-m values for p-nitrophenyl-beta-D-glucopyranoside of 90 and 500 mu M, respectively. Isozyme activities were adversely affected by several reported beta-glucosidase inhibitors, various metal ions, and lignin-derived aromatic acids and aldehydes. Glucose production from microcrystalline cellulose by a commercial cellulase preparation was enhanced by 9.7% in reaction mixtures supplemented with BGL-II. (C) 1998 Elsevier Science Inc.