The Effect of Cholesterol on the Lateral Diffusion of Phospholipids in Oriented Bilayers
2003 (English)In: Biophysical Journal, Vol. 84, 3079-86 p.Article in journal (Refereed) Published
Pulsed field gradient NMR was utilized to directly determine the lipid lateral diffusion coefficient for the following macroscopically aligned bilayers: dimyristoylphosphatidylcholine (DMPC), sphingomyelin (SM), palmitoyloleoylphosphatidylcholine (POPC), and dioleoylphosphatidylcholine (DOPC) with addition of cholesterol (CHOL) up to 40 mol %. The observed effect of cholesterol on the lipid lateral diffusion is interpreted in terms of the different diffusion coefficients obtained in the liquid ordered (lo) and the liquid disordered (ld) phases occurring in the phase diagrams. Generally, the lipid lateral diffusion coefficient decreases linearly with increasing CHOL concentration in the ld phase for the PC-systems, while it is almost independent of CHOL for the SM-system. In this region the temperature dependence of the diffusion was always of the Arrhenius type with apparent activation energies (EA) in the range of 28–40 kJ/mol. The lo phase was characterized by smaller diffusion coefficients and weak or no dependence on the CHOL content. The EA for this phase was significantly larger (55–65 kJ/mol) than for the ld phase. The diffusion coefficients in the two-phase regions were compatible with a fast exchange between the ld and lo regions in the bilayer on the timescale of the NMR experiment (100 ms). Thus, strong evidence has been obtained that fluid domains (with size of µm or less) with high molecular ordering are formed within a single lipid bilayer. These domains may play an important role for proteins involved in membrane functioning frequently discussed in the recent literature. The phase diagrams obtained from the analysis of the diffusion data are in qualitative agreement with earlier published ones for the SM/CHOL and DMPC/CHOL systems. For the DOPC/CHOL and the POPC/CHOL systems no two-phase behavior were observed, and the obtained EA:s indicate that these systems are in the ld phase at all CHOL contents for temperatures above 25°C.
Place, publisher, year, edition, pages
2003. Vol. 84, 3079-86 p.
IdentifiersURN: urn:nbn:se:umu:diva-16777OAI: oai:DiVA.org:umu-16777DiVA: diva2:156450