Conformation examination of uridine diphosphoglucose using lanthanide-nitrilotriacetate chelates as shift probes

A 13C NMR study utilizing the lanthanide-induced shift (LIS) technique was carried out on uridine diphosphoglucose (UDPG) in order to determine the solution conformation. The neutral, water soluble nitrilotriacetate chelates, Ln(NTA), were used in preference to the bare ions due to the potency of the latter in hydrolyzing the UDPG. In addition to the primary binding site at the pyrophosphate moiety, secondary binding to the uracil carbonyl groups was observed and found to be a function of the size of the lanthanide ion; the largest ions showed the greatest relative affinity for the carbonyl groups. This effect was overcome by extrapolating the observed shift ratios to zero Ln(NTA)/[UDPG]. The extrapolated shift ratios were relatively constant for a series of five lanthanides indicating the solution conformation of UDPG is insensitive to metal ion size. The conformation of the UDPG was found to be extended so that the uracil carbons as well as carbons 1', 2', and 3' of the ribose are outside of the pseudo-contact shift cone with the remaining carbons inside the cone.