The members of this family catalyse the formation of glucose 1-phosphate from one of the following polyglucoses; glycogen, starch, glucan or maltodextrin.

1: Control of phosphorylase b conformation by a modified cofactor: crystallographic studies on R-state glycogen phosphorylase reconstituted with pyridoxal 5'-diphosphate. Leonidas DD, Oikonomakos NG, Papageorgiou AC, Acharya KR, Barford D, Johnson LN; Protein Sci 1992;1:1112-1122. PMID:1304390