Physical properties of liposomes and proteoliposomes prepared from Escherichia coli polar lipids

Reconstituted protroliposomes serve as experimental systems for the study o f membrane enzymes. Osmotic shifts and other changes in the solution enviro nment may influence the structures and membrane properties of phospholipid vesicles (including liposomes, proteoliposomes and biological membrane vesi cles) and hence the activities of membrane-associated proteins. Polar lipid extracts from Escherichia coli are commonly used in membrane protein recon stitution. The solution environment influenced the phase transition tempera ture and the diameter of liposomes and proteoliposomes prepared from E, col i polar lipid by extrusion. Liposomes prepared from E. coli polar lipids di ffered from dioleoylphosphatidylglycerol liposomes in Young's elastic modul us, yield point for solute leakage and structural response to osmotic shift s, the latter indicated by static light scattering spectroscopy. At high co ncentrations, NaCl caused aggregation of E. coli lipid liposomes that precl uded detailed interpretation of light scattering data. Proteoliposomes and liposomes prepared from E. coli polar lipids were similar in size, yield po int for solute leakage and structural response to osmotic shifts imposed wi th sucrose as osmolyte. These results will facilitate studies of bacterial enzymes implicated in osmosensing and of other enzymes that are reconstitut ed in E. coli lipid vesicles. (C) 2000 Elsevier Science B.V. All rights res erved.