Lateral order in mixed lipid bilayers and its influence on ion translocation by gramicidin: a model for the structure-function relationship in membranes.
The temperature-composition phase diagram of dimyristoylphosphatidylcholine and dipentadecylphosphatidylglycerol (DiC15PG) was determined by mass densitometry. For a mixture containing 30 mol% DiC15PG, the homogeneous distribution of the 2 components is demonstrated in the fluid state at T = 35 degrees C by small-angle neutron scattering in combination with the inverse contrast variation method. By the same technique, the coexistence of fluid and condensed phases at T = 23.3 degrees C could be shown in agreement with the densitometric data. Furthermore, it is demonstrated that Ca++ induces, even at T = 35 degrees C, separation into 2 fluid phases. A corresponding phase separation is found in bimolecular lipid membranes ("black films") by analysis of the single-channel conductance fluctuations of gramicidin A incorporated into an equimolarly mixed membrane of neutral lecithin and charged phosphatidic acid. The results are discussed as primary examples on the model-membrane level for the important structure-function relationship of biomembranes.
Henkel
T
T
Technische Universität München, Physik-Department, Garching, FRG.
Mittler
S
S
Pfeiffer
W
W
Rötzer
H
H
Apell
H J
HJ
Knoll
W
W
D002118:Calcium / Q000494:pharmacology; D003217:Conductometry; D006096:Gramicidin; D007477:Ions; D008051:Lipid Bilayers; D008567:Membranes, Artificial; D010539:Permeability; D013329:Structure-Activity Relationship; D013696:Temperature; D013816:Thermodynamics
D007477:Ions; D008051:Lipid Bilayers; D008567:Membranes, Artificial; D006096:Gramicidin; D002118:Calcium