An enzyme that hydrolyzes 1,6-alpha-glucosidic branch linkages in glycogen, amylopectin, and their beta-limit dextrins. It is distinguished from pullulanase (EC 126.96.36.199) by its inability to attack pullulan and by the feeble action of alpha-limit dextrins. It is distinguished from amylopectin 6-glucanohydrolase (EC 188.8.131.52) by its action on glycogen. With EC 184.108.40.206, it produces the activity called "debranching enzyme". EC 220.127.116.11.