-!- The first reaction of this enzyme is to catalyze its own glucosylation, normally at a specific Tyr of the protein if this group is free; when the Tyr is replaced by Thr or Phe, the enzyme's 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 2.4.1.11. -!- 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. hydrolyzing 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. -!- Formerly EC 2.4.1.112.