The influence of Ca2+ on the lateral lipid distribution and phase transition in phosphatidylethanolamine/phosphatidylserine vesicles.

The lateral lipid distribution within dipalmitoylphosphatidylethanolamine (DPPE)/dipalmitoylphosphatidylserine (DPPS) vesicle membranes was investigated under the influence of Ca2+ using a lipid cross-linking method. To characterize the phase transition in DPPE/DPPS vesicles and to correlate the different phase states of the membrane lipids with the obtained lipid distribution ESR measurements using a fatty acid spin label were carried out. It is shown that Ca2+ has a significant influence on the lateral lipid distribution within the fluid phase of the membrane lipids; instead of a slight alternating lipid arrangement in absence of Ca2+ due to the electrostatic interaction between the DPPS headgroups after addition of Ca2+ a lateral cluster structure is characteristic of the fluid phase.