H-1-NMR SPECTROSCOPY STUDY OF THE DYNAMIC PROPERTIES OF GLYCOGEN IN SOLUTION BY STEADY-STATE MAGNETIZATION MEASUREMENT WITH OFF-RESONANCE IRRADIATION

The dynamics of size-selected fractions of glycogen in solution have b een investigated by proton NMR spectroscopy, using a recently describe d relaxation study method which relies on strong off-resonance irradia tion. The dependence of the steady-state magnetisation on angle and in tensity of the effective radio-frequency field was measured and compar ed to theoretical curves derived from different models of motion. Abse nce or presence of contributions to relaxation from molecular motions on the microsecond time scale can be tested with this method, without having to resort to models. We found that glycogen dipolar relaxation did not result from isotropic Brownian rotation, and despite some cont ribution from slow motion (>1 mu s) to relaxation in glycogen alpha-pa rticles extracted from rat liver, bulk movement of the molecules did n ot appear to participate in averaging the dipolar term to zero. Wherea s hepatic glycogen rat beta-particles and commercial oyster glycogen d isplayed very similar relaxation properties, alpha-particles showed si gnificantly different behaviour. However, all results were compatible with a diversity of movements within the molecule, ranging from freely rotating pyranoside rings through collective chain motion and possibl y to bulk movement of the beta sub-units within the alpha-particle. (C ) 1998 Elsevier Science Ltd. All rights reserved.