Effects of incorporation of various amphiphiles into recipient liposome membranes on inter-membrane protein transfer

To obtain information about the factors governing spontaneous inter-membran e protein transfer, we examined the effects of incorporation of various amp hiphilic compounds in dimyristoylphosphatidylcholine (DMPC) liposomes on pr otein transfer from influenza virus-infected cells to the liposomes, and an alyzed the physical properties of these liposome membranes. The incorporati on of amphiphilic compounds, negatively charged dicetylphosphate (DCP), dip almitoylphosphatidylserine (DPPS) or positively charged dimethyldipalmitoyl ammonium (DMDPA), into DMPC liposomal membranes enhanced protein transfer. The liposomes containing DCP, DPPS or DMDPA were unaffected by osmotic shoc k caused by external addition of glucose, suggesting a decrease in lipid pa cking in the liposomal membranes. Furthermore, calorimetric study of these liposomes showed that a phase separation occurred partially in the liposoma l membranes. Accordingly, the membranes of DMPC liposomes containing DCP, D PPS and DMDPA should be distorted due to the coexistence of two phases, gel and liquid crystalline, in the membranes. Consequently, the membrane disto rtion could be responsible for the enhancement effects of the amphiphiles o n the inter-membrane protein transfer from influenza virus-infected cells t o the liposomes.