Carotenoids in Lipid Membranes - Carotenoids: Physical, Chemical, and Biological Functions and Properties - page 25

consisting of the conjugated double-bond system of the polyene chain that appears to mediate the
effect on the membrane system. The interactions of rigid carotenoid molecules with alkyl lipid
chains, which undergo fast molecular motions (including the gauche-trans isomerization), restricts
the lipid motional freedom and therefore modulates the l uidity of the lipid bilayer in the l uid
phase. On the other hand, the membrane-bound carotenoids can destabilize the ordered lipid matrix
in the gel phase. The actual effect of carotenoids with respect to the lipid membranes (ordering
or l uidization) depends also on the chemical structure of the carotenoid that is incorporated. The
latter determinant is mostly based on the presence of the polar groups that can be anchored in
the polar zones of the lipid bilayer. For example, the incorporation of β -carotene and astaxanthin

((3 R ,3 -dione) at 5 mol% into the lipid membranes composed of

DOPC:cholesterol (molar ratio 1:5) result in very different effects on the membrane structure, as
demonstrated by the small angle x-ray scattering (McNulty et al., 2007). In the cases involving
astaxanthin, the electron density proi le across the membrane, was almost unaffected. By contrast,
β

′ R )-3,3 ′ -dihydroxy- β , β -carotene-4,4 ′

-carotene markedly affected the order of the hydrophobic core, especially in the central region.
The effect of lycopene was even stronger than that observed in the case of -carotene, particularly

in the methyl group region of alkyl chains (McNulty et al., 2007). The differences observed directly
correlate with the orientation of the carotenoid pigment with respect to the membrane, as discussed
earlier. The effect of carotenoid pigments on different membrane segments can also be analyzed by
means of 1 H-NMR spectroscopy (Gabrielska and Gruszecki, 1996; Sujak et al., 2005) or 13 C-NMR
and 31 P-NMR technique, based on the natural abundance of the 13 C and 31 P isotopes (Jezowska
et al., 1994). One aspect of the NMR studies is based on the analysis of the resonance lineshape
that rel ects the molecular dynamics of a particular group located at dei ned membrane zone, for
example, the CH 3 groups located in the central region of the bilayer (Gabrielska and Gruszecki,
1996; Jezowska et al., 1994; Sujak et al., 2005). Figure 2.4 presents the analysis of the width of the
1 H-NMR band corresponding to the terminal methyl groups of the alkyl chains of the membranes
modii ed with

β

β -carotene and canthaxanthin ( β , β -carotene-4,4 ′ -dione). Broadening of the band,

20

16

12

Canthaxanthin

8

4

β-carotene

0

0 0.4 0.8 1.2 1.6

Carotenoid content (mol%)

FIGURE 2.4 Carotenoid presence-induced increase in the full width at half height of the 1 H-NMR band
corresponding to the CH 3 groups of alkyl chains of liposomes formed with EYPC and containing β-carotene
and formed with DPPC and containing canthaxanthin. (Based on Gabrielska, J. and Gruszecki, W.I., Biochim.
Biophys. Acta, 1285, 167, 1996; Sujak, A. et al., Biochim. Biophys. Acta, 1712, 17, 2005.)