Catalysis of the 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. Substrates include laminarin, lichenin and cereal D-glucans.
glucan endo-1,4-beta-glucanase activity, C-3 substituted reducing group