Spin label EPR study of lipid solvation of supramolecular photosynthetic protein complexes in thylakoids

Anabella Ivancich, LászlóI I. Horváth, Magdolna Droppa, Gábor Horváth, Tibor Farkas

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Abstract

Lipid-protein association in the chloroplast membrane and its various thylakoid fractions from higher plants, namely pea and maize, rich in Photosystem I (PSI) and Photosystem II (PSII), respectively, were studied using EPR spectroscopy of spin-labelled lipid molecules. All the EPR spectra consisted of two spectral components corresponding to bulk fluid lipids and solvation lipids motionally restricted at the hydrophobic surface of membrane proteins. Spin-labelled stearic acid and phosphatidylglycerol exhibited marked selectivity towards the supramolecular protein complexes of both PSI and PSII although to different extent. In addition, lipid-protein titration experiments are described for partially delipidated PSII-enriched membrane fractions of pea chloroplasts, incorporating unlabelled egg phosphatidylcholine prior to or after the incorporation of spin-labelled lipids. Two sets of solvation sites were resolved by timed labelling experiments and a significant result of these studies was that a well-defined population of solvation sites (approx. 100 mol lipids/820 kDa protein) was rapidly exchanged by laterally diffusing membrane lipids, while other solvation sites (approx. 50 mol lipids/820 kDa protein) were exchanged much slower or not exchanged at all.

Original languageEnglish
Pages (from-to)51-56
Number of pages6
JournalBBA - Biomembranes
Volume1196
Issue number1
DOIs
Publication statusPublished - Nov 23 1994

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Keywords

  • EPR
  • Lipid-protein interaction
  • Thylakoid

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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