Influence of pH on phosphatidic acid multilayers. A rippled structure at high pH values

Area of Science:

• Biochemistry
• Lipid Bilayer Structure
• Physical Chemistry

Background:

• Phosphatidic acid is a key phospholipid involved in cell signaling and membrane structure.
• The physical properties of lipid bilayers are sensitive to environmental factors like pH and ionic strength.
• Understanding lipid polymorphism is crucial for comprehending membrane function.

Purpose of the Study:

• To investigate the structural influence of high pH on 1,2-(ditetradecyl)-phosphatidic acid (DTPA) bilayers.
• To characterize the phase behavior and structural transitions of DTPA at alkaline pH.

Main Methods:

• Differential scanning calorimetry (DSC) to analyze thermal transitions.
• Freeze-fracture electron microscopy (FFEM) to visualize bilayer morphology.

Main Results:

• At high pH (13.5-14, 2.6 M K+), DTPA exhibits a pretransition below its main phase transition temperature.
• FFEM revealed regular, ripple-like band patterns in DTPA bilayers quenched from below the main phase transition temperature.
• The observed rippled structure is analogous to that found in phosphatidylcholine bilayers.

Conclusions:

• High pH induces a distinct structural organization in DTPA bilayers, characterized by a rippled phase.
• The findings suggest that the charge state of phosphatidic acid significantly impacts its structural polymorphism.
• The structural similarity to phosphatidylcholines highlights conserved mechanisms of lipid bilayer self-assembly under specific conditions.