Hydrodynamic radii and lipid transfer in prostasome self-fusion

The characteristics of human prostasomal vesicles have been investigated by three methods, namely, dynamic light scattering, transfer of a lipophylic fluorescent dye (R18), and electron microscope appearance. The vesicle preparations were stable for a long time and their diameters were in the range of 200 nm. The exposure to acidic pH values (about 5) increased both particle radii and the transfer of R18. The microscopic appearance was also affected by the pH value. We infer that these changes are due to a self-fusion of prostasome vesicles; this fusion is protein-dependent since various methods used by us and able to affect the protein component of membranes (boiling, extraction of lipid and liposome preparation, treatment with pronase) all abolished the effect seen at pH 5 on intact particles.