This entry covers several enzymes from different sources that act in vivo on different forms of (1->4)-alpha-D-glucans. Some of these enzymes catalyse the first step in the degradation of large branched glycan polymers - the phosphorolytic cleavage of alpha-1,4-glucosidic bonds from the non-reducing ends of linear poly(1->4)-alpha-D-glucosyl chains within the polymers. The enzyme stops when it reaches the fourth residue away from an alpha-1,6 branching point, leaving a highly branched core known as a limit dextrin. The accepted name of the enzyme should be modified for each specific instance by substituting "glycogen" with the name of the natural substrate, e.g. maltodextrin phosphorylase, starch phosphorylase, etc.