The accepted name varies according to the source of the enzyme and the nature of its synthetic product (cf. EC 188.8.131.52, phosphorylase). Glycogen synthase from animal tissues is a complex of a catalytic subunit and the protein glycogenin. The enzyme requires glucosylated glycogenin as a primer; this is the reaction product of EC 184.108.40.206 (glycogenin glucosyltransferase). A similar enzyme utilizes ADP-glucose (EC 220.127.116.11, starch synthase).