Isolation, enzymatic properties, and mode of action of an exo-1,3-beta-glucanase from Trichoderma viride

An exo-1,3-beta-glucanase has been isolated from cultural filtrate of T. viride AZ36. The N-terminal sequence of the purified enzyme (m = 61 +/- 1 kDa) showed no significant homology to other known glucanases. The 1,3-beta-glucanase displayed high activity against laminarins, curdlan, and 1,3-beta-oligoglucosides, but acted slowly on 1,3-1,4-beta-oligoglucosides. No significant activity was detected against high molecular mass 1,3-1,4-beta-glucans. The enzyme carried out hydrolysis with inversion of the anomeric configuration. Whereas only glucose was released from the nonreducing terminus during hydrolysis of 1,3-beta-oligoglucosides, transient accumulation of gentiobiose was observed during hydrolysis of laminarins. The gentiobiose was subsequently degraded to glucose. The Michaelis constants Km and Vmax have been determined for the hydrolysis of 1,3-beta-oligoglucosides with degrees of polymerization ranging from 2 to 6. Based on these data, binding affinities for subsites were calculated. Substrate binding site contained at least five binding sites for sugar residues.