Synergistic effects of Ca2+ and wheat germ agglutinin on the lamellar‐hexagonal (HII) phase transition of glycophorin‐containing egg‐phosphatidylethanolamine membranes

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Abstract
Glycophorin has been reconstituted into egg phosphatidylethanolamine (egg‐PtdEtn) membranes. Stable vesicles were obtained at a molar ratio of 8 × 10−4 of inserted protein/lipid. This macroscopic change from lipid aggregates to lipid vesicles was followed by density gradient centrifugation. Vesicles formed in the presence of protein enclose the dye calcein and are stable with time and temperature. Membrane aggregation does not occur, as was demonstrated by energy‐transfer experiments. The phase transition from the fluid lamellar Lα phase to the inverted hexagonal HII phase observed at 29°C in pure egg‐PtdEtn membranes is suppressed and finally disappears in the presence of glycophorin. The transition enthalpy decreases linearly from ΔH= 4 kJ/mol in pure lipids to zero at a protein/lipid molar ratio of 1:1000. Ca2+ ions and wheat germ lectin act synergistically on the phase behavior of vesicles containing glycophorin and phosphatidylethanolamine. Differential scanning calorimetry scans show that the lamellar‐to‐hexagonal phase transition is reinduced. The membranes aggregate and exchange lipid as could be demonstrated by energy transfer experiments. The dye calcein is released but only if the temperature exceeds the lamellar‐to‐hexagonal phase transition temperature of the pure egg‐PtdEtn.