Polymorphism of the 1-Palmitoyl-2-arachidonoyl-phosphatidyl-ethanolamine/Dimyristoyl-phosphatidylmethanol Mixture, a Phospholipase A2 Substrate

Abstract

The polymorphism of the equimolar mixture of 1-palmitoyl-2-arachidonoyl-phosphatidylethanolamine (PAPE) and dimyristoyl-phosphatidylmethanol (DMPM) was examined by infrared and31P nuclear magnetic resonance spectroscopy to determine the suitability of this widely used but yet uncharacterized lipid mixture as a phospholipase A2 substrate. The results show that the mixture undergoes a gel-to-liquid crystalline phase transition between 12 and 35°C. The transitions of the individual lipids were also examined. We report that the temperature of the gel-to-liquid crystalline phase transition of DMPM is 40°C. At 2°C, PAPE exists in the fluid lamellar form. This lipid undergoes a lamellar-to-inverted hexagonal phase transition at 31°C. In conclusion, the equimolar PAPE/DMPM mixture forms fluid lamellar phase at the physiological temperature. However, the upper end of the gel-to-liquid crystalline phase transition of the mixture is really close to the physiological temperature and this situation is a serious source of potential artefacts.