||The first reaction of this enzyme is to catalyse its own glucosylation, normally at Tyr-194 of the protein if this group is free. When Tyr-194 is replaced by Thr or Phe, the enzyme’s Mn2+-dependent self-glucosylation activity is lost but its intermolecular transglucosylation ability remains . It continues to glucosylate an existing glucosyl group until a length of about 5–13 residues has been formed. Further lengthening of the glycogen chain is then carried out by EC 18.104.22.168, glycogen (starch) synthase. The enzyme is not highly specific for the donor, using UDP-xylose in addition to UDP-glucose (although not glucosylating or xylosylating a xylosyl group so added). It can also use CDP-glucose and TDP-glucose, but not ADP-glucose or GDP-glucose. Similarly it is not highly specific for the acceptor, using water (i.e. hydrolysing UDP-glucose) among others. Various forms of the enzyme exist, and different forms predominate in different organs. Thus primate liver contains glycogenin-2, of molecular mass 66 kDa, whereas the more widespread form is glycogenin-1, with a molecular mass of 38 kDa.
||Krisman, C.R. and Barengo, R. A precursor of glycogen biosynthesis: α-1,4-glucan-protein. Eur. J. Biochem. 52 (1975) 117–123. [DOI] [PMID: 809265]
||Pitcher, J., Smythe, C., Campbell, D.G. and Cohen, P. Identification of the 38-kDa subunit of rabbit skeletal muscle glycogen synthase as glycogenin. Eur. J. Biochem. 169 (1987) 497–502. [DOI] [PMID: 3121316]
||Pitcher, J., Smythe, C. and Cohen, P. Glycogenin is the priming glucosyltransferase required for the initiation of glycogen biogenesis in rabbit skeletal muscle. Eur. J. Biochem. 176 (1988) 391–395. [DOI] [PMID: 2970965]
||Kennedy, L.D., Kirkman, B.R., Lomako, J., Rodriguez, I.R. and Whelan, W.J. The biogenesis of rabbit-muscle glycogen. In: Berman, M.C. and Opie, L.A. (Eds), Membranes and Muscle, ICSU Press/IRL Press, Oxford, 1985, pp. 65–84.
||Rodriguez, I.R. and Whelan, W.J. A novel glycosyl-amino acid linkage: rabbit-muscle glycogen is covalently linked to a protein via tyrosine. Biochem. Biophys. Res. Commun. 132 (1985) 829–836. [DOI] [PMID: 4062948]
||Lomako, J., Lomako, W.M. and Whelan, W.J. A self-glucosylating protein is the primer for rabbit muscle glycogen
biosynthesis. FASEB J. 2 (1988) 3097–3103. [PMID: 2973423]
||Alonso, M.D., Lomako, J., Lomako, W.M. and Whelan, W.J. Catalytic activities of glycogenin additional to autocatalytic self-glucosylation. J. Biol. Chem. 270 (1995) 15315–15319. [DOI] [PMID: 7797519]
||Alonso, M.D., Lomako, J., Lomako, W.M. and Whelan, W.J. A new look at the biogenesis of glycogen. FASEB J. 9 (1995) 1126–1137. [PMID: 7672505]
||Mu, J. and Roach, P.J. Characterization of human glycogenin-2, a self-glucosylating initiator of liver glycogen metabolism. J. Biol. Chem. 273 (1998) 34850–34856. [DOI] [PMID: 9857012]
||Gibbons, B.J., Roach, P.J. and Hurley, T.D. Crystal structure of the autocatalytic initiator of glycogen biosynthesis, glycogenin. J. Mol. Biol. 319 (2002) 463. [DOI] [PMID: 12051921]