Phase behavior of ether lipids from Clostridium butyricum

Ether lipids have been isolated from the phospholipid fraction of Clostridium butyricum IFO 3852 cells which had been grown in media devoid of biotin with added elaidic acid or oleic acid. The plasmalogen form of phosphatidylethanolamine (plasmenylethanolamine) from elaidate-grown cells was highly enriched with 18:1 in both the alk-1-enyl and acyl chains. A transition from the gel to liquid-crystalline state, with a peak maximum (Tm) at 33 degrees C and enthalpy delta H = 5.7 kcal/mol, was observed by differential scanning calorimetry. With the fluorescent probes cis- and trans-parinaric acids, transitions were observed at 33 degrees C on heating and at 29 degrees C on cooling. These transition temperatures are 5-6 degrees C lower than those reported for the corresponding diacyl lipid, dielaidoylphosphatidylethanolamine. A similar study of the phase behavior of both the elaidate-enriched and oleate-enriched glycerol acetal derivative of plasmenylethanolamine from C. butyricum revealed a large hysteresis of 12.5-16 degrees C. Hysteresis in the polar head group motion was also observed by 31P nuclear magnetic resonance. The elaidate-enriched lipid, which melted between 28 and 33 degrees C, appears to undergo supercooling prior to the transition to the gel state at about 18-13 degrees C, depending on the scanning rate. The formation of a more ordered gel state relative to plasmenylethanolamine was indicated by a 2-fold increase in delta H. Electron microscopy revealed a marked reorganization from typical multilamellar liposomes above Tm to large needle-like structures below Tm. The oleate-enriched glycerol acetal lipid formed the gel phase at -4 degrees C, which is 10 degrees C above the transition temperature reported for dioleoylphosphatidylethanolamine. Stabilization of oleate-enriched glycerol acetal lipid bilayers may result from hydrogen bonding between polar head groups. The relationship of the phase behavior of the ether lipids to the lipid composition and phase behavior of C. butyricum membranes is discussed.