It catalyzes the chemical reactions: Thus, the two substrates of this enzyme are UDP-alpha-D-glucose and glycogenin, whereas its two products are UDP and alpha-D-glucosylglycogenin.

Glycogenin was discovered in 1984 by Dr. William J. Whelan, a fellow of the Royal Society of London and former professor of Biochemistry at the University of Miami.

Evidence accumulates that a priming protein may be a fundamental property of polysaccharide synthesis in general; the molecular details of mammalian glycogen biogenesis may serve as a useful model for other systems.

Glycogenin is able to use the other two pyrimidine nucleotides as well, namely CDP-glucose and TDP-glucose, in addition to its native substrate, UDP-glucose.

Patients have been found with defective GYG1, resulting in muscle cells with the inability to store glycogen, and consequential weakness and heart disease.