Removes maltotriose and maltotetraose chains that are attached by 1,6-alpha-linkage to the limit dextrin main chain, generating a debranched limit dextrin. Shows only very little activity with native glycogen. Hydrolysis of (1->6)-alpha-D-glucosidic linkages to branches with degrees of polymerization of three or four glucose residues in limit dextrin. Inhibited by iodoacetate, p-chloromercuribenzoate, HgCl(2), cupric sulfate and ammonium sulfate. Optimum pH is 5.6 to 6.4. Optimum temperature is 45-50 degrees Celsius. Glycan degradation; glycogen degradation. Monomer. Disruption of the gene leads to overproduction of glycogen containing short external chains. Belongs to the glycosyl hydrolase 13 family. Truncated C-terminus.