In 1984 we demonstrated that glycogen is covalently bound to a protein constituting the so-called proteoglycogen. In 1985 we described that glycogen is bound to a tyrosine residue of the protein in a new type of glycosidic linkage. There after other groups demonstrated that the
glycogen-bound protein, named glycogenin, is an autoglucosyltransferase that initiates the polymerization of glucose, synthesizing the primer for further polymerization by glycogen synthase. We described and characterized a biosynthetic precursor of proteoglycogen associated to membrane and postulated it might be the product of the de novo biosynthesis of glycogen that initiates in membrane. The hypothesis is consistent with our recent demonstration of the amphiphilic character of glycogenin. This property would allow the association of glycogenin to membrane before beginning with the glucose polymerization. We have also described the isolation of the C-chain bound to glycogenin (c-glycogenin), the modulation of glycogenin expression during development and its thermal stabilization and inhibition of glucosyltransferase activity caused by linkage to the polysaccharide. Our interest is currently focused on the study of: a) the structure of the glycogenin-glycogen synthase complex by X ray diffraction; b) the amphiphilicity of glycogenin related to the degree of polymerization of the linked glucan; c) the degree of polymerization of the C-chain of c-glycogenin; d) the initiation of the de novo biosynthesis of glycogen in prokaryote; the incorporation of the first glucose into the tyrosine residue of glycogenin.