STEADY-STATE FLUORESCENCE QUENCHING FOR DETECTING ACYL-CHAIN INTERDIGITATION IN PHOSPHATIDYLCHOLINE VESICLES

In the present study we have demonstrated the detection of the transit ion of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) multilamella r vesicles from the noninterdigitated gel to the fully interdigitated gel phase in the presence of ethanol or ethylene glycol (EG) using the method of fluorescence quenching. This method is based on the change of accessibility of 2-(12-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl)amino)do decanoyl - 1 - hexadecanoyl-sn-glycero-3-phophatidyl-choline (NBD-PC), a membrane-buried fluorophore, to iodide, a quencher in the aqueous s olution, during the phase transition. It is found that accessible fluo rophore appears to increase at ethanol and EG concentrations known for inducing DPPC interdigitation. This increase in accessibility is eith er due to the relocation of the fluorescent moiety closer to the lipid -water interface or an increase in the ability of the quencher to pene trate into the loosely packed headgroup region of the interdigitated d omain or both. Our results suggest the coexistence of interdigitated a nd noninterdigitated phases in the phospholipid vesicles and the metho d of fluorescence quenching might be useful in quantitating the percen tage of phospholipids which are interdigitated. (C) 1997 Elsevier Scie nce B.V.