Farnesol-DMPC phase behaviour: a (2)H-NMR study.

Involved in a number of diverse metabolic and functional contexts, farnesol is a central component of the mevalonate pathway, post-translationally attaches to proteins, and affects a number of other membrane-associated events. Despite farnesol's biological implications, a detailed analysis of how farnesol affects the physical properties and phase behaviour of lipid membranes is lacking. As (2)H-NMR spectra are sensitive to molecular motions and acyl chain orientation, they can be used to measure the degree of molecular order present in the system. Also, since the (2)H-NMR spectra of fluid and gel phase lipids are very different, they are sensitive probes of membrane phase equilibrium and can be used to determine fluid-gel phase boundaries. In this study, dimyristoyl phosphatidylcholine-d(54) (DMPC-d(54)) bilayers containing varying concentrations of trans-trans farnesol (2.5-20.0 mol%) are investigated over a range of temperatures (8-30 degrees C). Analysis of these spectra has led to the construction of a farnesol-DMPC-d(54) temperature-composition plot. We show that increasing concentrations of farnesol induce a decrease in the fluid-gel phase transition temperature and promote fluid-gel coexistence. Interestingly, farnesol does not seem to affect the quadrupolar splittings (Delta v(Q)) in the fluid phase, i.e., the organization of farnesol within the bilayer and its interaction with phospholipids does not appreciably influence acyl chain order in the fluid phase.