Catalytic properties and mode of action of three endo-beta-glucanases from Talaromyces emersonii on soluble beta-1,4- and beta-1,3;1,4-linked glucans

摘要

In this paper, we present the first detailed analysis of the modes of action of three purified, thermostable endo-beta-D-glucanases (EG V-VII) against a range of soluble beta-linked glucans. Studies indicated that EG V-VII, purified to homogeneity from a new source, the thermophilic fungus Talaromyces emersonii, are strict beta-glucanases that exhibit maximum activity against mixed-link 1,3; 1,4-beta-D-glucans. Time-course hydrolysis studies of 1,4-beta-D-glucan (carboxymethylcellulose; CMC), 1,3;1,4-beta-D-glucan from barley (1313G) and lichenan confirmed the endo-acting nature of EG V-VII and verified preference for 1,3; 1,4-beta-D-glucan substrates. The results suggest that EG VI and EG VII belong to EC 3.2.1.6, as both enzymes also exhibit activity against 1,3-beta-glucan (laminaran), in contrast to EG V. Although cellobiose, cellotriose and glucose were the main glucooligosaccharide products released, the range and relative amount of each product was dependent on the particular enzyme, substrate and reaction time. Kinetic constants (K-m, V-max, k(cat) and k(cat)/K-m) determined for EG V-VII with BBG as substrate yielded similar K-m and V-max values for EG V and EG VI. EG VII exhibited highest affinity for BBG (K-m value of 9.1 mg ml(-1)) and the highest catalytic efficiency (k(cat)/K-m of 12.63 s(-1) mg(-1) ml). (C) 2003 Elsevier B.V. All rights reserved. [References: 21]