EPR Spin Labeling in Carotenoid–Membrane Interactions - Carotenoids: Physical, Chemical, and Biological Functions and Properties - page 205

10.6 HOW THE MEMBRANE ITSELF AFFECTS DISTRIBUTION
AND LOCALIZATION OF CAROTENOIDS IN THE LIPID
BILAYER (LOW CAROTENOID CONCENTRATION)

10.6.1 A CCUMULATION OF P OLAR C AROTENOIDS IN U NSATURATED M EMBRANE D OMAINS
It was recently demonstrated that macular xanthophylls are substantially excluded from mem-
brane domains enriched in saturated lipids and cholesterol (raft domains) and remain 8-14 times
more concentrated in the bulk domain, which is enriched in unsaturated lipids (Wisniewska and
Subczynski 2006a,b). A similar distribution was observed for -caro-

tene, which is more uniformly distributed between these domains (Figure 10.12). This distribution
was demonstrated using cold Triton X-100 extraction from membranes containing 1 mol

β -cryptoxanthin, but not for β

of caro-
tenoids. The saturation-recovery EPR DOT method was also used in these investigations showing
that membrane domains are not the artifacts created by the Triton X-100 and the low temperature,
but they exist in situ at physiological temperatures, indicating additionally. Results also demonstrate
that macular xanthophylls, at 1 mol

%

do not affect the formation of these domains (Wisniewska and
Subczynski 2006a,b). The location of xanthophylls in membrane domains formed from unsaturated
lipids (illustrated in Figure 10.13) is ideal if they are to act as a lipid antioxidants, which is the most

%

4 4

β-CAR
β-CXT
LUT
ZEA

β-CAR
β-CXT
LUT
ZEA

3 3

2 2

1

1

0 0

DRM DSM DRM DSM

FIGURE 10.12 The mole ratio of carotenoid/phospholipid and carotenoid/total lipid (phospholipid + cho-
lesterol) in raft domain (detergent-resistant membrane, DRM) and bulk domain (detergent-soluble membrane,
DSM) isolated from membranes made of raft-forming mixture (equimolar ternary mixture of dioleoyl-PC
(DOPC)/sphingomyelin/cholesterol) with 1 mol% lutein (LUT), zeaxanthin (ZEA), β-cryptoxanthin (β-CXT),
or β -carotene ( β -CAR).

Bulk domain
(unsaturated lipids)

Raft domain
(saturated lipids)

Lutein
zeaxanthin SM DOPC Cholesterol

FIGURE 10.13 Schematic drawing of the distribution of xanthophyll molecules between raft domain (DRM)
and bulk domain (DSM) in lipid bilayer membranes. For this illustration, the xanthophyll partition coefi cient
between domains is the same as obtained experimentally for raft-forming mixture. However, to better visu-
alize the observed effect in the drawing, the number of lipid molecules was decreased and the total number
of xanthophyll molecules was increased about 10 times. (From Wisniewska, A. and Subczynski, W.K., Free
Radic. Biol. Med ., 40, 1820, 2006. With permission.)