Uridine sugar nucleotides modified in their nucleoside moieties and their effect on lipid-linked saccharide formation in vitro.

Uridine diphospho glucose (UDP-Glc) and uridine diphospho N-acetylglucosamine (UDP-GlcNAc), modified in the uridine moiety by either periodate oxidation of the ribose ring or substitution at position 5 of the uracil ring with fluorine, have been tested as potential inhibitors of glucosyl monophosphoryl dolichol (Glc-P-Dol) or N,N-diacetylchitobiosyl pyrophosphoryl dolichol [GlcNAc)2-PP-Dol) assembly in chick embryo cell membranes. The periodate oxidised sugar nucleotides inhibited glycosyl transfer from their respective natural counterparts by 50% at 230 micron periodate oxidised UDP-Glc and 70 micron periodate oxidised UDP-GlcNAc respectively. Inhibition in both cases was irreversible and addition of exogenous Dol-P stimulated only the residual non-inhibited reaction. Periodate oxidised UDP-GlcNAc preferentially inhibited the transfer of GlcNAc to GlcNac-PP-Dol. The sugar nucleotide containing 5-fluorouridine were, on the other hand, alternative substrates for Glc-P-Dol or (GlcNAc)2-PP-Dol synthesis. FUDP-Glc was a good substrate for Glc-P-Dol formation; having Km and Vmax values equal to those of UDP-Glc, whereas FUDP-GlcNAc was a less efficient substrate for the formation of (GlcNAc)2-PP-Dol; having Km and Vmax values one half and one third respectively of those of UDP-GlcNAc.