Abstract
On annealing at 5°C of a gel phase temperature, multilamellar vesicles of dimyristoylphosphatidylglycerol (DMPG) prepared in the presence of 1M NaCl at pH 7.0 converted to well-developed crystalline cylindrical structures similar to those formed by Ca2+-bound DMPG. The new crystalline phase transformed into the liquid crystal phase at 44.2°C. The transition enthalpy (∼19kcal/mol) is about 2.5 times larger than that of the MLV gel to liquid crystal phases, suggesting a large contribution of pseudo lattice enthalpy to the chain-melting transition of Na+-bound DMPG in the present system. The conversion process of the MLV gel to cylindrical crystalline phases with an increase in annealing time was investigated by electron microscopy and it was found that a set of membranes (8-9 lamellae) separated from the MLV surface grows into helical superstructures and, subsequently, into the final cylindrical structures.
