Gramicidin effects on the transverse and lateral distribution of pyrene and pyrene derived probes in lipid bilayers

The excimer to monomer fluorescence intensity ratios obtained by direct excitation and by energy transfer from protein intrinsic tryptophan to pyrene and the enhancement of the 0-0 vibration transition in the monomer 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 dynamics of these probes in bilayers of small unilamellar vesicles consisting of egg yolk phosphatidylcholine (EPC) and gramicidin containing EPC liposomes (proteoliposomes). Our measurements reveal that gramicidin does not influence the lateral distribution of PD but reduces the PD excimer formation in the protein environment. On the contrary, PM enriches in the vicinity of gramicidin probably as a result of a fluidity gradient from the phospholipid headgroup region to the protein environment. Pyrene molecules preferentially reside in the neighbourhood of gramicidin for the same reason as given for PM, but are kept away from gramicidin at temperatures below 25 degrees C owing to the rigidity of the outer regions of the membrane.