Thermotropic behavior of dipalmitoylphosphatidylcholine vesicles reconstituted with the glycoprotein of vesicular stomatitis virus

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Abstract
The vesicular stomatitis virus glycoprotein reconstituted into dipalmitoylphosphatidylcholine (DPPC) vesicles exerts a profound effect upon the DPPC gel to liquid-crystalline phase transition. The glycoprotein was reconstituted into DPPC vesicles by octyl glucoside dialysis. The gel to liquid-crystalline phase transition of these vesicles was monitored by differential scanning calorimetry. Vesicles formed in the absence of glycoprotein (600-2100 .ANG. diameter) underwent the phase transition at 41.0.degree. C and had an associated enthalpy change of 8.0 .+-. 1.6 kcal/mol. Increasing the mole ratio of glycoprotein to DPPC in the vesicles to 0.15 mol% reduced both the transition temperature and the transition enthalpy change. The enthalpy change as a function of the mole percent glycoprotein could be fit to a straight line by a least-squares procedure. Extrapolation of the results to the glycoprotein concentration where the enthalpy change was zero indicated 1 glycoprotein molecule bound 270 .+-. 150 molecules of DPPC.