(a) Sialyltransferase (SiaT) assay based on transfer of FITCNeuAc from CMP-FITCNeuAc to N-linked (ST6Gal I, ST3Gal III) and O-linked (ST3Gal I) glycans of asialo-fetuin. (b) Fucosyltransferase (FUT) assay based on transfer of a fluorescent fucose analog from GDP-FLUORFuc to an N-glycan on fetuin. (c) Time course of ST3Gal III-mediated transfer of FITCNeuAc to asialo-fetuin produces increased fluorescence polarization over time, and is inhibited by the known competitive inhibitor, CDP. (d) Time-course of the FUT7 fluorescence polarization assay using GDP-FLUORFuc, fetuin, and FUT7, and inhibition by the known competitive inhibitor GDP.