Conformational studies of sphingolipids by NMR spectroscopy. II. Sphingomyelin

Sphingomyelin (SM) Is the most prevalent sphingolipid in the majority of ma mmalian membranes. Proton and P-31 nuclear magnetic resonance spectral data were acquired to establish the nature of Intra- and intermolecular H-bonds in the monomeric and aggregated forms of SM and to assess possible differe nces between this lipid and dihydrosphingomyelin (DHSM). which lacks the do uble bond between carbons 4 and 5 of the sphingoid base. The spectral trend s suggest the formation of an intramolecular H-bond between the OH group of the sphingosine moiety and the phosphate ester oxygen of the head group. T he narrower linewidth and the downfield shift of the resonance correspondin g to OH proton in SM suggest that this H-bond is stronger in SM than in DHS M. The NH group appears to be involved predominantly in intramolecular H-bo nding In the monomer. As the concentration of SM increases and the molecule s come in closer proximity, these intramolecular bonds are partially disrup ted and the NH group becomes involved in lipid-water interactions. The diff erence between the SM and DHSM appears to be not in thr nature of these int eractions but rather in the degree to which these intermolecular Interactio ns prevail. As SM molecules cannot come as close together as DHSM molecules can, both the NH and OH moieties remain, on average. more intramolecularly bonded as compared to DHSM. (C) 2000 Elsevier Science B.V, All rights rese rved.