Identification of Carotenoids in Photosynthetic Proteins: Xanthophylls of the Light Harvesting Antenna - Carotenoids: Physical, Chemical, and Biological Functions and Properties - page 130

of the antenna (Ruban et al., 2002a). It is interesting to note, the n 4 region for xanthophyll cycle
carotenoids bound to the minor antenna complexes, CP26 and CP29, reveals little structure despite
the fact that they remain bound in these complexes under higher detergent conditions (Ruban et al.,
2002a). Therefore it is feasible to assume that the n 4 i ngerprint rel ects binding of the xanthophyll
within a specii c site—any dislocation from this site can cause structural relaxation of the molecule
without necessarily inducing its detachment from the protein.

7.8 IDENTIFICATION OF ACTIVATED ZEAXANTHIN IN THE
PHOTOPROTECTIVE STATE OF ANTENNA
NPQ described in the Section 7.5.3 is always accompanied by the appearance of a small absorption
change at around 535 nm (Deamer et al., 1967; Heber, 1969). The amplitude of this band correlates
linearly with the nonradiative energy dissipation parameter, k D , which was described earlier (Ruban
et al., 1993). The 535 nm band has been frequently attributed to selective light scattering, which
appears upon the establishment of the proton gradient across the thylakoid membrane (Heber,
1969). The maximum position of this band has now been found to depend upon the presence of
zeaxanthin (Noctor et al., 1993). The absorption peaks near 535 nm in the membranes or leaves
with zeaxanthin, and is blueshifted toward 525 nm without zeaxanthin. In addition, the amplitude
of the 535 nm band was discovered to be in a good correlation with the amount of zeaxanthin
(Ruban et al., 1993b).
These observations implicating the role of zeaxanthin in the formation of the 535 nm band have
prompted us to test the nature of this absorption feature using the resonance Raman excitation
near its maximum (argon line at 528.7 nm). Figure 7.11a presents the n 1 resonance Raman spectral

1.25

WT +NPQ

Light

1.00

0.75

Dark

0.50

Light-dark

0.25

0.00

NPQ mutant -NPQ

1.00

Dark

0.75

Light

0.50

0.25

Light-dark

Trimer 1 Trimer 2

0.00

1490 1500 1510 1520 1530 1540 1550 1560

(b)

(a)

Wavenumber (cm -1 )

FIGURE 7.11 Identii cation of redshifted zeaxanthin associated with nonphotochemical chlorophyll l uores-
cence quenching. (a) Resonance Raman spectra in the n 1 region for the wild type (+NPQ) and NPQ4 mutant
(−NPQ) chloroplasts. Light: 15 min illumination with 1000 mM ∙ m −2 ∙ s −1 light. Dark: 10 min recovery after the
illumination. (b) Structure of two interacting LHCII trimers displaying a possible interaction giving rise to the
formation of the J-type xanthophyll aggregate.