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 Tric hoderma 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 -oligoglucosid es. No significant activity was detected against high molecular mass 1,3-1, 4-beta -glucans. The enzyme carried out hydrolysis with inversion of the an omeric configuration. Whereas only glucose was released from the nonreducin g terminus during hydrolysis of 1,3-beta -oligoglucosides, transient accumu lation of gentiobiose was observed during hydrolysis of laminarins. The gen tiobiose was subsequently degraded to glucose. The Michaelis constants K-m, and V-max have been determined for the hydrolysis of 1,3-beta -oligoglucos ides with degrees of polymerization ranging from 2 to 6. Based on these dat a, binding affinities for subsites were calculated. Substrate binding site contained at least five binding sites for sugar residues.