Carbon-13 nuclear magnetic resonance study of spin labelled cholesteryl ester in model membranes.

Carbon-13 NMR longitudinal relaxation times for unilamellar vesicles of egg phosphatidylcholine (PC) in aqueous dispersion have been measured following the incorporation of spin labelled cholesteryl palmitate. The spin label induced relaxation rates, 1/T1,SL, for fatty acyl chain carbons show that the C5 segment of the cholesteryl ester acyl chain is located near the C1 and C2 segments of the phospholipid acyl chains. A greater spin label induced enhancement of relaxation rate was observed for the inner vesicle layer than for the outer, and is attributed to a higher ester incorporation and/or tighter lipid packing in the inner layer.