Isolation and characterization of a thermostable endo-beta-glucanase active on 1,3-1,4-beta-D-glucans from the aerobic fungus Talaromyces emersonii CBS 814.70

A novel endoglucanase active on 1,3-1,4-beta -D-glucans was purified to app arent homogeneity from submerged cultures of the moderately thermophilic ae robic fungus Talaromyces emersonii CBS 814.70. The enzyme is a single subun it glycoprotein with M-r and pI values of 40.7 +/- 0.3 kDa and 4.4, respect ively, and an estimated carbohydrate content of 77% (w/w). The purified bet a -glucanase displayed activity over broad ranges of pH and temperature, yi elding respective optima values of pH 4.8 and 80 degreesC. This enzyme was markedly thermostable with 15% of the original activity remaining after inc ubation for 15 min at 100 degreesC. Substrate specificity studies revealed the identity of the enzyme to be a 1,3-1,4-beta -D-glucanase. Identical K-m values (13.38 mg.ml(-1)) were obtained with lichenan and BEG, while the V- max value with lichenan (142.9 IU.mg(-1)) was approximately twice the value obtained with BEG (79.3 IU.mg(-1)). Time-course hydrolysis of barley-beta -glucan did not proceed linearly with respect to time indicating an 'endo' or more processive action for the enzyme. HPAEC fractionation of the produc ts of hydrolysis yielded a range of oligosaccharides, with cellobiose, cell otriose and cellotetraose being the predominant oligosaccharide products. ( C) 2001 Elsevier Science Inc. All rights reserved.