THE USE OF FLUORESCEINPHOSPHATIDYLETHANOLAMINE (FPE) AS A REAL-TIME PROBE FOR PEPTIDE MEMBRANE INTERACTIONS

The characterization of fluoresceinphosphatidylethanolamine (FPE) as a real-timid indicator of the electrostatic nature of a membrane surfac e is described. The conditions appropriate for the labelling of membra nes and the implementation of FPE as a tool to monitor the interaction s of various peptides with model membranes are outlined. It is shown t hat of the membrane-active peptides studied, Naja naja kaouthia cardio toxin and pyrularia thionin bind to certain model membranes without in sertion. Whereas the leader sequence of the nuclear encoded subunit IV of mammalian cytochrome c oxidase (E.C. 1.9.3.1), known as p-25, and melittin appear to bind and then partially insert into the membrane. I t seems evident also that melittin does not adopt a fully transmembran e configuration. Melittin is known to promote membrane! lysis and by e mploying a rapid-kinetic technique it is shown that the time-course of such lysis does not appear to correlate with peptide binding, but fol lowing binding a significant proportion of melittin must become insert ed into the membrane before lysis appears to commence.