Buffer-Induced Swelling and Vesicle Budding in Binary Lipid Mixtures of Dioleoylphosphatidylcholine:Dioleoylphosphatidylethanolamine and Dioleoylphosphatidylcholine:Lysophosphatidylcholine Using Small-Angle X-ray Scattering and 31P Static NMR

A large variety of data exists on lipid phase behavior; however, it is mostly in nonbuffered systems over nonbiological temperature ranges. We present biophysical data on lipid mixtures of dioleoylphosphatidylcholine (DOPC), dioleoylphosphatidylethanolamine (DOPE), and lysophosphatidylcholine (LysoPC) examining their behaviors in excess water and buffer systems over the temperature range 4–34 °C. These mixtures are commonly used to investigate the effects of spontaneous curvature on integral membrane proteins. Using small-angle X-ray scattering (SAXS) and 31P NMR, we observed lamellar and vesicle phases, with the buffer causing an increase in the layer spacing. Increasing amounts of DOPE in a DOPC bilayer decreased the layer spacing of the mesophase, while the opposite trend was observed for increasing amounts of LysoPC. 31P static NMR was used to analyze the DOPC:LysoPC samples to investigate the vesicle sizes present, with evidence of vesicle budding observed at LysoPC concentrations above 30 mol %. NMR...