Glucocerebroside transfer between phosphatidylcholine bilayers

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Abstract
The kinetics of transfer of glucocerebroside between phospholipid bilayers were studied 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 containing 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 half-time [t1/2] of transfer from donor DMPC-PyrCer vesicles to acceptor DMPC vesicles is > 30 days at 37.degree. 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 2 vesicle populations by molecular sieve chromatography at 45.degree. C shows a t1/2 for transfer of .apprx. 2 days. In contrast to the results obtained for phosphatidylcholines, glucocerebroside does not rapidly transfer between bilayers under these conditions.