Endoglucanases are most often referred to in the context of cellulases. Though these enzymes have a high affinity toward cellulose, they often exhibit cross reactivity with other p-glucans, including xyloglucan and mixed p-(1 —>3,1—4)-glucans. As with the endoxylanases, these enzyme cleave p-(1—4) or p-(1 —— 3) linkages in the interior of the glucose chain, generating two new chain ends, one reducing and one non-reducing. Different enzymes are required to cleave the two forms of p-glucan (28, 30-35). Enzymatic degradation of p-glucan is accomplished through glycosyl hydrolase family 12 enzymes (EC 3.2.1.4). Although these endo-acting enzymes are active on p-(1——4) glycosidic linkages, they are differentiated from other p-(1—4)-acting enzymes by being able to hydrolyze the p-(1——4) linkages in mixed p-(1—3,1—4)-linked polysaccharides. Glucan endo-1,3-p-D-glucosidase [p-(1——3) glucanase] (EC 3.2.1.39) is an endo-acting glycosyl hydrolase that acts on p-(1——3) glucan, but has very limited activity on the mixed linkage p-glucan. Endo-1,3(4)-p-glucanase [p- (1—3, 1—4) glucanase] (EC 3.2.1.6), is also an endo-acting glycosyl hydrolase. There is an exo-acting glycosyl hydrolase that is active on p-(1——3) glucan. Glucan 1,3-p-glucosidase (EC 3.2.1.58) acts by processively releasing glucose from p-(1 —— 3) glucan from the non­reducing end.

Much of the initial work on cellulases and endoglucanases was concentrated on the en — zymology of the fungus Trichoderma reesei. This fungus produces several cellulases which act synergistically in the degradation of cellulose. In T. reesei, the Cel7B is a major endoglu — canase, forming about 6-10% of the total T. reesei cellulase (36, 37). It has wide activity against solid and soluble substrates, such as CMC, as well as against xylan and glucoman — nans (38). Also, the endoglucanase Cel5A has activity against solid (celluloses) and soluble (CMC, mannan) substrates (39-41), but not on xylans. This enzyme comprises up to 10% of the total cellulases in T. reesei (36, 37). The minor endoglucanases (Cel12A, Cel45A) are reported to hydrolyze solid and soluble (including glucomannan) substrates with diverse specific activities.