Endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans. Optimum pH is 5.2. Active from pH 4.5 to 6.5. The N- and the C-terminus may be subjected to proteolysis. One Trp residue has been proved to be involved in the mechanism of action of endo-K. Belongs to the glycosyl hydrolase 8 (cellulase D) family.