Glucocerebroside transfer between phosphatidylcholine bilayers.

We have studied the kinetics of transfer of glucocerebroside between phospholipid bilayers by using pyrene and 3H-labeled glucocerebroside incorporated into dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) bilayers. Pyrene-labeled glucocerebroside (PyrCer) molecules are able to form an excited complex (eximer, E) between a PyrCer in the ground state and an excited monomer (M). When vesicles contained a known amount of PyrCer (donors) are incubated with unlabeled vesicles (acceptors), transfer of PyrCer from donor to acceptor populations is reflected in a decrease of the observed E/M intensity ratio. The results obtained from these studies show that the half-time of transfer from donor DMPC-PyrCer vesicles to acceptor DMPC vesicles is greater than 30 days at 37 degrees C. This very slow transfer of glucocerebroside was confirmed by using tritiated glucocerebroside incorporated into small unilamellar DPPC donor vesicles incubated with large unilamellar DPPC acceptor vesicles above the phase transition. Separation of the two vesicle populations by molecular sieve chromatography at 45 degrees C shows a half-time for transfer of approximately 32 days. We conclude that, in contrast to the results obtained for phosphatidylcholines [Roseman, M., & Thompson, T. E. (1980) Biochemistry 19, 439], glucocerebroside does not rapidly transfer between bilayers under these conditions.