Protein-dependent Reduction of the Pyrene Excimer Formation in Membranes |
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Authors: | M Engelke P Bojarski HA Diehl A Kubicki |
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Institution: | (1) Institute of Experimental Physics, FB1, University of Bremen, D-28334 Bremen, Germany, DE;(2) Institute of Experimental Physics, Wita Stwosza 57, 80-952 Gdansk, Poland, PL |
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Abstract: | The presence of proteins in lipid bilayers always decreases the excimer formation rate of pyrene and pyrene lipid analogues
in a way that is related to the protein-to-lipid ratio. Energy transfer measurements from intrinsic tryptophans to pyrene
have shown (Engelke et al., 1994), that in microsomal membranes, the excimer formation rate of pyrene and pyrene fatty acids
is heterogeneous within the membrane plane, because a lipid layer of reduced fluidity surrounds the microsomal proteins. This
study investigates whether of not liposomes prepared from egg yolk phosphatidylcholine with incorporated gramicidin A give
results comparable to those from microsomal membranes. The results indicate that the influence of proteins on the lipid bilayer
cannot be described by one unique mechanism: Small proteins such as gramicidin A obviously reduce the excimer formation rate
by occupying neighboring positions of the fluorescent probe and thus decrease the pyrene collision frequency homogeneously
in the whole membrane plane, while larger proteins are surrounded by a lipid boundary layer of lower fluidity than the bulk
lipid.
The analysis of the time-resolved tryptophan fluorescence of gramicidin A incorporated liposomes reveals, that the tryptophan
quenching by pyrene is stronger for tryptophans located closely below the phospholipid headgroup region because of the pyrene
enrichment in this area of the lipid bilayer.
Received: 29 December 1996/Revised: 15 May 1996 |
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Keywords: | : Energy transfer — Intrinsic tryptophans — Pyrene excimer formation — Membrane fluidity — Gramicidin incorporated liposomes — Microsomal membranes |
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