glycogenin

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Function

glycogenin functions as a primer for glycogen synthesis
glycogen is a self glucosylating enzyme that uses UDP-glucose to link glucose to one of its own Tyr
glucosylated glycogenin then serves as a nucleus for synthesis of glycogen
glycogen synthase has a low Km for large glycogen molecules; however, Km increases as the glycogen decreases in size, such that very small glycogen molecules & glucose itself do not function as substrates for glycogen synthesis at physiologic concentrations
glycogenin is phosphorylated by cAMP-dependent protein kinase

↑ Textbook of Biochemistry with Clinical Correlations, 3rd ed., TM Devlin (ed), Wiley-Liss, NY 1992 pg 345