Phosphorylase is an important allosteric enzyme in carbohydrate metabolism. Enzymes from different sources differ in their regulatory mechanisms and in their natural substrates. However, all known phosphorylases share catalytic and structural properties (By similarity). Required for glycogen breakdown in skeletal muscle. [(1->4)-alpha-D-glucosyl](n) + phosphate = [(1->4)-alpha-D-glucosyl](n-1) + alpha-D-glucose 1-phosphate Phosphorylation of Ser-15 converts phosphorylase B (unphosphorylated) to phosphorylase A. Belongs to the glycogen phosphorylase family.