NMR-STUDIES OF H-1 NOES IN GLYCOGEN

We have examined the cross-relaxation behavior among the protons of oy ster glycogen using nuclear Overhauser enhancement (NOE). Steady-state and transient NOEs were generated using low-power CW irradiation and frequency-selective inversions. In D2O, saturation of glycogen H2 and H4' at 3.64 ppm gave a strong negative NOE (eta = -0.74) at H1. The NO E was similar to the value predicted by the correlation time (tau(c)) calculated from the T1 and T2 of glycogen H1 in D2O assuming an isotro pic rigid motor dipole-dipole model. Selective inversion of H2 and H4' gave a transient NOE at H1. In D2O, selective inversion of H1 also le d to negative transient NOEs in the H2+H4', H3, and H5 resonances. The magnitude and rates of appearance of the NOEs in H3 and H5 were too l arge to arise from direct H1-H3 and H1-H5 dipolar interactions, but we re consistent with very efficient cross-relaxation leading to large se cond-order NOEs. The glycogen H1 NOE in H2O was also studied. Replacem ent of D2O with H2O as solvent significantly reduced the steady-state NOE at H1 following saturation of H2+H4'. Saturation of the water reso nance caused a large negative NOE at H1 (eta = -0.55) consistent with our earlier study which indicated that there was no direct dipolar int eraction between H1 and free H2O.