Studies on the phase transitions of lysoderivatives of ethanolamine glycerophospholipids from human brain

The phase transition temperature of 1,2-distearoylglycerophosphocholine is reduced in presence of equimolar amounts of 1-O-(1'-alkenyl)-glycerophosphoethanolamine (ethanolamine lysoplasmalogen) from 53.3 degrees C-54.1 degrees C to 44.0 degrees C-44.9 degrees C at different pH (4.0; 7.2; 9.0; 10.5). 1-Acyl-glycerophosphoethanolamine leads to a smaller reduction of the 1,2-distearoyl-glycerophosphocholine transition temperature: 45.0 degrees C-46.2 degrees C at the same pH-values. 1-Alkyl-glycerophosphoethanolamine (hydrogenated ethanolamine lysoplasmalogen) possesses a transition temperature, which is 3.3 degrees C-4.9 degrees C higher than the hydrogenated 1-acyl-glycerophosphoethanolamine at each pH investigated. At pH 9.0 and, more pronounced, at pH 10.5 we find a reduction of the transition temperature for both these substances, whereas their transition temperature is nearly unchanged at pH 4.0 and 7.2. Our results clearly show that the ether-bonding in the lysoderivative of plasmalogen is responsible for the closer packing compared to the 1-acyl-glycerophosphoethanolamine.