Natural abundance carbon-13 nuclear magnetic resonance studies of bovine white matter and myelin

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Abstract
Whole bovine white matter yielded a poorly resolved natural abundance 13C NMR spectrum. The spectrum principally reflected C atoms of the constituent membrane lipids: several resonances could be specifically assigned but no resonances attributable to cholesterol were detectable. Except for the methyl group at the terminus of fatty acyl chains, lipid C giving rise to the 13C NMR spectrum had values of spin-lattice relaxation time between 140-500 ms, indicating significant restrictions on segmental and rotational mobilities but consistent with a generally fluid structural organization. The 13C NMR spectrum of myelin isolated from bovine white matter was similar to that for the whole white matter itself. In both white matter and isolated myelin, the integrated intensities for several C atoms were considerably less than those for the same C atoms in total lipid extracts. The data for white matter and myelin were consistent with a model in which observed line broadening is due to restrictions in the amplitude of chain flexing rather than to severe restrictions on chain segmental motion. Failure to detect resonances of cholesterol ring system C atoms may reflect marked anisotropy of rotational reorientation.