Calorimetric detection of a membrane-lipid phase transition in living cells.

The membrane lipids in living Mycoplasma laidlawii exhibit a phase transition characteristic of that from crystal to liquid crystal within the bilayer conformation. The transition occurs at the same temperature in viable organisms, membranes isolated from the organisms, and isolated membrane lipids. The enthalpy of the transition in the membrane is compared with that of an aqueous suspension of isolated membrane lipids. The result is consistent with presence of an extended lipid bilayer in the native membrane.