(I) The Baculovirus Expression Vector System was employed for the expression of N-acetylglucosaminyl transferases in Sf9 insect cells. UDP-GlcNAc:alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I (GnT I), a key enzyme in the biosynthesis of the beta(1,2)-linkage between GlcNAc and the Man-alpha(1,3)-Man branch of the core mannose trisaccharide of N-glycans, and UDP-GlcNAc:alpha-6-D-mannoside beta-1,2-N-acetylglucosaminyltransferase II (GnT II) involved in the transfer of GlcNAc from UDP-GlcNAc to the Man-alpha(1,6)-Man branch of the same glycan, were expressed and partially purified. GnT I was tested in an enzymic reaction that yielded a homogeneous sample of the tetrasaccharide, D-mannose-alpha(1,6)-[N-acetyl-D-glucosamine-beta(1,2)-D-mannose-alpha(1,6)]- beta-O-methyl-D-mannoside, which was structurally characterized by 1D 1H and 13C NMR spectroscopy, and 2D 13C-1H HMQC experiments. The primary goal of this work is to establish reliable methodology for the enzymic synthesis of 13C-labeled oligosaccharides needed for structural studies by NMR spectroscopy.(II) Protein-Amadori intermediates, the products of reaction of the primary amino groups of proteins with the acyclic aldehyde form of glucose, gradually convert into several advanced glycation end-products (AGEs) which lead to nephropathy and many other diseases. The reactive intermediates and advanced glycation end-products have not been fully characterized and mechanisms of their formation remains to be elucidated. Protein-Amadori can be prepared in vitro from proteins and D-glucose in the presence of pyridoxamine, an intermediate of vitamin B metabolism, which inhibits the formation of glycation endproducts. Detailed NMR analysis of spontaneously forming intermediates of the glycation pathway (after the removal of pyridoxamine) can provide valuable information about their chemical identity and kinetics of their formation if suitable isotopically-labeled samples are available. Ubiquitin, a small eukaryotic and archaebacterial protein, has been proposed as a model protein to study the formation of advanced glycation end-products because of the limited number of its sugar-exposed lysines and its well-characterized structure. Expression of 15N- (and 15N/13C)-labeled ubiquitin in E. coli and purification of this protein to homogeneity for the use in NMR studies of protein glycation are presented in this chapter.(III) One or more molecules of sialic acid (SA) are often found on the terminal non-reducing ends of biologically important oligosaccharides. These SA residues are often attached to the remaining oligosaccharide via alpha-2,3-O-glycosidic bonds. The conformational properties of glycosidic bonds involving SA are difficult to investigate by NMR spectroscopy, but proper isotopic labeling with 13C can improve the situation by making new experimental parameters such as 3JCOCC available. The enzyme, alpha-2,3-(N)-sialyltransferase, can be used to install SA onto a growing oligosaccharide chain provided that the substrate, cytidine-5'-monophospho-N-acetylneuraminic acid (CMP-SA), is available. Reported here is the enzymic synthesis of CMP-SA catalyzed by CMP-sialic acid synthetase from sialic acid and CTP. This method will be used to prepare 13C-labeled CMP-SA for use in the preparation of labeled sialylated oligosaccharides found in the N-glycan on the FC domain of human IgG.