INTERACTION OF ENANTIOMERS OF LYSYL-7-AZATRYPTOPHYL-LYSINE WITH ACIDIC PHOSPHOLIPID-VESICLES - A FLUORESCENCE STUDY

A tripeptide containing a single 7-azatryptophan (7AW) residue was syn thesized with the use of racemic 7AW and purified by high-performance liquid chromatography (HPLC), The peptide NH2-lysyl-7-aza-tryptophyl-l ysine (K7AWK) is analogous to the peptide lysine-tryptophyl-lysine (KW K) whose interactions with acidic lipids are well characterized, It ha s not been possible to achieve the separation of 7AW D and L enantiome rs under HPLC conditions that normally are used to separate enantiomer s of amino acids. HPLC of the peptide, however, indicated that there w ere two main components of nearly equal concentration in the partially purified synthetic peptides. Thin-layer chromatography, paper electro phoresis, amino acid analysis, and steady-state absorption and fluores cence spectra showed that the two HPLC peaks corresponded to peptides with the same composition bat with different enantiomers of 7AW. Time- resolved fluorescence measurements of the purified enantiomers indicat ed that there were differences in the excited-state decay parameters. The nature of the interaction of the different enantiomers of the basi c peptide with vesicles of the acidic lipid palmitoyl-oleoyl phosphati dylserine (POPS) at pH 5.0 has been elucidated with the use of steady- state fluorescence measurements. Interaction of the peptide with vesic les in the liquid crystalline phase suggested that proton transfer fro m the POPS to the 7AW occurs, resulting in enhanced emission at 450 nm . These results are compared to those from the Trp containing peptide KWK, and the unique advantages of 7AW as a spectroscopic probe are des cribed.