Thermotropic properties of dispersions of cholesterol with tetraether lipids from Thermoplasma acidophilum.

The main glycophospholipid from Thermoplasma acidophilum is composed of a diisopranol-2,3-glycerotetraether. The fraction of pentane cyclizations of its hydrocarbon chains increases with the growth temperature of the source organism (39-59 degrees C). Hydrated mixtures of these lipids together with cholesterol have been studied by calorimetry. With the reduction of the phase transition temperatures and enthalpy changes of the transitions, cholesterol is readily incorporated into lipid monolayers in the liquid-crystalline and the (metastable) solid-analogue phase. Lipid samples with a high number of acyclic hydrocarbon chains form a stable and a metastable solid-analogue phase. With the increasing concentration of cholesterol the metastable solid-analogue phase is stabilized and the time constant for the formation of the stable solid-analogue phase is prolonged.