This enzyme hydrolyzes cellotetraose, cellopentaose, and cellohexaose to cellobiose and cellotriose but does not hydrolyze cellobiose or cellotriose. Endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans. Optimum pH is 6.8 with carboxymethyl cellulose (CmC) as substrate. Optimum temperature is 60 degrees Celsius with carboxymethyl cellulose (CmC) as substrate.