Endomannanases (EC 3.2.1.78) catalyze the random hydrolysis of p-D-1,4 mannopyranosyl linkages within the main chain of mannans and various polysaccharides consisting mainly of mannose, such as glucomannans and galactoglucomannans. Far fewer mannanases are characterized as compared with the numerous xylanases. The mannanase of Trichoderma reesei has a similar multi-domain structure to several cellulolytic enzymes; i. e., the protein contains a catalytic core domain which is connected by a linker to a cellulose-binding domain (20,21). The CBD increases the action of T. reesei mannanase onfiber-bound glucomannan, even though the catalytic domain can efficiently degrade crystalline mannan (22).

The main hydrolysis products from galactoglucomannans and glucomannans are manno — biose, mannotriose, and various mixed oligosaccharides. The hydrolysis yield is dependent on the degree of substitution as well as on the distribution of the substituents (23). The hydrolysis of glucomannans is also affected by the glucose to mannose ratio. Some man — nanases are able to hydrolyze not only the (3 -1,4-bond between two mannose units, but also the bond between the adjacent glucose and mannose units (24,25). Interestingly, some mannanases are able to degrade mannan crystals quite efficiently (26, 27).

Enzymes needed for further hydrolysis of the released manno-oligomers produced by endoenzymes are p-mannosidase (1,4-p-D-mannoside mannohydrolase, EC 3.1.1.25) and p-glucosidase (EC 3.2.1.21). p-mannosidase and p-glucosidase catalyze the hydrolysis of manno-oligosaccharides by removing successive mannose or glucose residues from the non-reducing termini. The p — xylosidase of T. reesei and p — mannosidases of A. niger are also able to attack polymeric xylan and mannan, respectively, liberating xylose and mannose by successive exo-action (28, 29).