The present invention relates to an enzyme-catalyzed process for producing UDP-N-acetyl-α-D-glucosamine (UDP-GlcNAc) from low-cost substrates uridine monophosphate and N-acetyl-D glucosamine in a single reaction mixture with immobilized or preferably co-immobilized enzymes. Uridine may be used as starting material instead of uridine monophosphate as well. Further, the process may be adapted to produce GlcNAcylated molecules and biomolecules including saccharides, particularly human milk oligosaccharides (HMO), proteins, peptides, glycoproteins, particularly antibodies, or glycopeptides, and bioconjugates, particularly carbohydrate conjugate vaccines and antibody-drug conjugates.