Diene-Containing Lipids as Probes for Phase-Transition Behavior of Lipids in Liposomes

Article abstract of DOI:10.1246/bcsj.62.102

The absorption maximum (λ_max) of 1,2-bis(2,4-octadecadienoyl)-sn-glycero-3-phosphorylcholine (DODPC), dispersed in an aqueous medium as liposomes, showed blue shift from 256.8 nm to 241.8 nm when these liposomes were cooled down from liquid crystalline state to gel state.The blue shift is explained to be due to stronger interaction between diene groups at gel state.This diene-containing lipid is examined to be an excellent membrane probe because it is typical phopholipid and miscible with several lipids.Furthermore, the dienoyl groups are known to be settled in the definite positions in bilayer membrane by suitable chemical modification.Phase transition behaviors of various 2,4-octadecadienoyl-containing phosphorylcholines as analogs for DODPC have also been investigated.Although they had similar spectral shifts at gel-to-liquid crystalline phase-transition temperature, their phase-transition temperatures and magnitude of λ_max shifts were revealed to be related directly and therefore be governed by the different packing of the diene groups in bilayer membrane.DODPC was mixed with 1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine, or cholesterol, and phase behaviors of these mixed liposomes were also examined.Phase-transition of the mixed liposomes was detected easily by the shift of its λ_max with high sensitivity.Results were quite comparable to those obtained from other measurements, such as DSC, NMR, and so on.