Tyrosine-194 of glycogenin undergoes autocatalytic glucosylation but is not essential for catalytic function and activity.

Glycogenin is the protein primer for glycogen synthesis. By autocatalytic transglucosylation from UDPglucose, it creates a malto-octaose chain attached to its Tyr-194. It has been uncertain whether the autocatalysis includes the addition of the first glucose residue to Tyr-194. We now show this to be the case. However, we also demonstrate, contrary to a claim by others, that Tyr-194 is not necessary for the catalytic function and activity of glycogenin.