GRAMICIDIN AFFECTS THE TRANSVERSE AND LATERAL DISTRIBUTION OF PYRENE AND PYRENE DERIVED PROBES IN LIPID BILAYERS

The excimer-to-monomer fluorescence intensity ratios obtained by direc t excitation and by energy transfer from protein intrinsic tryptophan to pyrene and the enhancement of the 0-0 vibration transition in the m onomer fluorescence spectra of pyrene, pyrene methanol (PM) and pyrene dodecanoic acid (PD) have been measured as a function of temperature and gramicidin concentration to investigate the localizations and dyna mics of these probes in bilayers of small unilamellar vesicles constit uted of egg yolk phosphatidylcholine (EPC) and gramicidin containing E PC liposomes (proteoliposomes). Our measurements reveal that gramicidi n does not influence the lateral distribution of PD but reduces the PD excimer formation in the protein environment. On the contrary, PM enr iches in the vicinity of gramicidin probably as a result of a fluidity gradient from the phospholipid headgroup region to the protein enviro nment. Pyrene molecules preferentially reside in the neighbourhood of gramicidin for the same reason as PM, but are kept away from gramicidi n at temperatures below 25 degrees C due to the rigidity of the outer regions of the membrane.