The control of glycoprotein synthesis: N-acetylglucosamine linkage to a mannose residue as a signal for the attachment of L-fucose to the asparagine-linked N-acetylglucosamine residue of glycopeptide from alpha1-acid glycoprotein.

Summary Rat liver microsomes catalyze the incorporation of L-fucose from GDP-L-fucose into a glycopeptide prepared from human plasma α1-acid glycoprotein; the glycopeptide must have terminal mannose-linked β-N-acetylglucosamine to be active as an acceptor but fucose does not become linked to this N-acetylglucosamine residue. Endo-β-N-acetyl-glucosaminidase treatment of the product of the reaction shows that the fucose is incorporated into the asparagaine-linked N-acetylglucosamine residue. Competition studies show that this focusyltransferase is the same enzyme as a GDP-flucose:β-N-acetylglucosaminide focusyltransferase previously described to be present in rat liver Golgi apparatus.