Interaction of tubulin with phospholipid vesicles. I. Association with vesicles at the phase transition.

Purified soluble tubulin will interact with highly sonicated small unilamellar vesicles of dipalmitoyl phosphatidylcholine. This results in the leakage of a fluorescent dye, carboxyfluorescein, from the internal aqueous space of the vesicles at the lipid phase transition. The amount of dye leaked from the vesicles is determined by the tubulin to vesicle ratio and partial dye leakage reflects the uniform leakage of carboxyfluorescein from all of the vesicles. Once tubulin interacts with dipalmitoyl phosphatidylcholine vesicles at the phase transition, it is unavailable to interact with additional vesicles. This interaction represents the formation of stable tubulin-vesicle recombinants as shown by density gradient centrifugation. Such recombinants are only formed by interacting the protein with the vesicles at the lipid phase transition temperature. The interaction is insensitive to ionic strength (0.001 to 4 M NaCl) and the recombinants remain stable for days.