Figure 4.

Reexamination of the resonance pattern observed in the −9.8 ppm resonance previously assigned exclusively to UDP-glucose. (A) A regional brain ³¹P spectrum showing the splitting features of resonance signals at −8.2 pm and −9.8 ppm. Note that the resonance pattern of the −9.8 ppm signal is not a simple doublet, suggesting the presence of additional UDP(G) species beside UDP-glucose. (B) (Bottom purple trace) UDP-glucose ³¹P signals at 7T simulated with aqueous solution NMR data (Δδ = 1.6 ppm and ²J_PP = 20.5 Hz) acquired at 202.5 MHz. (Top black trace) A brain ³¹P MR spectrum post-processed with a line-broadening factor of 25 Hz. Note the difference in span, splitting, and relative peak magnitude of the upfield doublet between the simulated and in vivo data. (C) Brain ³¹P MR spectra acquired at TR 5 s with (red trace) and without (black trace) wideband ¹H-decoupling, showing that the large splitting of the upfield signal at −9.8 ppm does not reflect weak ¹H-³¹P coupling. (D) Regional brain ³¹P spectra acquired at TR = 1 s (black trace) and 5 s (red trace), scaled to the signal at −9.8 ppm to facilitate comparison of resonance patterns. The bottom trace (gray) shows the spectral difference. Note the similarity in linewidth and relative intensity between the NAD(H) signal and the upfield signal at −9.8 ppm. Abbreviations: ATP, adenosine triphosphate; NAD(H), nicotinamide adenine dinucleotide; PCr, phosphocreatine; PDE, phosphodiesters; PME, phosphomonoesters; and PI, inorganic phosphate; UDP(G), a combination of UDP-Gal, UDP-Glc, UDP-GalNAc, and UDP-GlcNAc.