Mixed-linked glucanase involved in the degradation of complex natural cellulosic substrates. Active on laminarin. lichenan, soluble carboxymethyl cellulose but not on pustulan. Endohydrolysis of (1->3)- or (1->4)-linkages in beta-D-glucans when the glucose residue whose reducing group is involved in the linkage to be hydrolyzed is itself substituted at C-3. Belongs to the glycosyl hydrolase 16 family.