Phase Transitions of Phospholipids

Abstract

Much evidence has accumulated which indicates that phospholipid bilayers form an especially important part of the structure of biological membranes, as was first suggested by Danielli and Davson1 in 1935. For example, recent x-ray2 and calorimetric3,4 observations on the membranes of Mycoplasma laidlawii give strong support to the existence of the lipid bilayer structure in this micro-organism. Because of their probable significance in connection with the structure and function of biological membranes, phospholipids have in recent years been the subject of many studies by a wide variety of experimental techniques. This paper summarizes investigations of the thermal behavior of phospholipids utilizing high-sensitivity differential scanning calorimetry as the primary observational technique. This technique provides certain insights into the nature of the phase transitions of phospholipid bilayers which cannot be contained by any other method. Furthermore, it permits observations on much more dilute suspensions of phospholipids that can be handled by other techniques.