The effect of surface-bound protein on the permeability of proteoliposomes.
Proteoliposomes have been prepared from mixtures of dipalmitoylphosphatidylcholine and phosphatidylinositol by sonication (SUV) and reverse phase evaporation (REV) and conjugated with succinyl concanavalin A (sConA). The proteoliposomes were characterised in terms of size and composition and covered a range of size (weight-average diameter) from approx. 80 to 300 nm and surface-bound sConA (weight-average number of protein molecules per liposome) from approx. 200 to 1800. The permeabilities of the proteoliposomes to encapsulated D-glucose have been measured and found to increase linearly with protein conjugation. The D-glucose permeability also increases with temperature and passes through a maximum in the region of the gel to liquid-crystalline phase transition temperature. Conjugation has no effect on the chain-melting temperature but slightly decreases the enthalpy of the transition consistent with the withdrawal of some phospholipid participation in chain-melting. The D-glucose permeabilities and thermotropic properties of the proteoliposomes are discussed in terms of the dislocation of the bilayer by the possible off-axis motion of the lipid which anchors the protein to the liposomal surface.
Francis
S E
SE
Department of Biochemistry and Molecular Biology, University of Manchester, U.K.
Lyle
I G
IG
Jones
M N
MN
D003208:Concanavalin A / Q000031:analogs & derivatives / Q000737:chemistry; D005947:Glucose / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry*; D008565:Membrane Proteins / Q000737:chemistry*; D008956:Models, Chemical; D010539:Permeability; D013499:Surface Properties; D013816:Thermodynamics
D008081:Liposomes; D008565:Membrane Proteins; D003208:Concanavalin A; C019558:succinylconcanavalin A; D005947:Glucose