Chemistry Reference
In-Depth Information
10
EPR Spin Labeling in
Carotenoid-Membrane
Interactions
Witold K. Subczynski and Justyna Widomska
CONTENTS
10.1 Introduction ........................................................................................................................ 189
10.2 Handling the Sample for EPR Measurements .................................................................... 191
10.3 Conventional EPR............................................................................................................... 192
10.3.1 Alkyl Chain Order ................................................................................................ 192
10.3.2 Rotational Diffusion of Alkyl Chains................................................................... 193
10.3.3 Hydrophobicity ..................................................................................................... 195
10.3.4 Phase Transition .................................................................................................... 196
10.4 Saturation-Recovery EPR ...................................................................................................197
10.4.1 Oxygen Transport Parameter ................................................................................ 197
10.4.2 Discrimination by Oxygen Transport ................................................................... 199
10.4.3 Ion Penetration into the Membrane ......................................................................200
10.4.4 Alkyl Chain Bending ............................................................................................ 201
10.5 How Carotenoids Affect Membrane Properties (High Carotenoid Concentration) ........... 201
10.5.1 Do Carotenoids Regulate Membrane Fluidity? .................................................... 201
10.5.2 Barriers of Lipid Bilayers Formed by Polar Carotenoids ..................................... 203
10.5.3 Solubility of Carotenoids in Lipid Bilayer Membranes ........................................204
10.6 How the Membrane Itself Affects Distribution and Localization of Carotenoids
in the Lipid Bilayer (Low Carotenoid Concentration)........................................................ 205
10.6.1 Accumulation of Polar Carotenoids in Unsaturated Membrane Domains ........... 205
10.6.2 Transmembrane Localization of
cis
-Isomers of Zeaxanthin................................206
10.7 EPR Spin-Labeling Demonstrates Membrane Properties Signii cant for Chemical
Reactions and Physical Processes Involving Carotenoids .................................................. 207
Acknowledgments ..........................................................................................................................209
References ......................................................................................................................................209
10.1 INTRODUCTION
Carotenoids are synthesized by bacteria, algae, and plants where they serve as an antenna function in
light-harvesting complexes and photoreactive centers (Grifi ths et al. 1955, Sei rmann-Harms 1987,
Koyama 1991). The highest concentration of carotenoids was reported to occur in membranes of
bacteria living under extreme conditions (high or low temperatures, salinity, pH, and
or strong light)
(Huang and Haug 1974, Clejan et al. 1986, Chamberlain et al. 1991, Anton et al. 2002). Carotenoids
are also present at a fairly high concentration in the lipid bilayer portion of the thylakoid membrane
as a free component during the violaxanthin cycle where they affect membrane l uidity (Gruszecki
/
189
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