Nuclear magnetic resonance studies of polyisoprenols in model membranes

Abstract

2H-NMR investigation of polyisoprenols (PIs) in model membranes has revealed information about their motions, relative order, and locate within the membrane. Initial 2H-NMR studies of the organization of the shorter chain homologues geraniol (C 10), farnesol (C 15), and solanesol (C 45) were carried out by incorporating 2H-acetyl esters of the alcohol or the di-perdeuterome-thylated derivatives of the omega-labeled phenols into multilamellar phosphatidylcholine (PC) vesicles. 2H-NMR powder patterns interpretable in terms of quadrupole splittings and spin-lattice relaxation times were obtained. Similar experiments have now been carried out with the labeled free alcohol, acetyl ester, and phosphate ester of dolichol (C 95) and undecaprenol (C 55). 2H-NMR results show that the head and tail 2H-labeled sites of C 35 and C 95 exhibit a fast motion isotropic signal only; no slower motion anisotropy, as exhibited by the short chain PIs, was observed. These data suggest that C 55 and C 95 either havesubstantially different (faster motions and/or conformations relative to the shorter chain PIs within the membrane, and that the longer PIs alter the membrane host packing matrix. This conclusion was supported by 31P-NMR studies of C 55 and C 95 derivatives in PC and PE/PC membranes, which showed new pronounced spectral changes relative to the results obtained with the shorter chain PIs. These spectral changes indicate that undecaprenol and dolichol derivatives appear to induce a non-bilayer (isotropic) organization of phospholipid molecules in PE/PC (2:1) vesicles. The possible physiological consequences of this perturbation remains to be determined.