Xanthophylls distortion

Xanthophyll distortion revealed by Raman spectroscopy may not only be an important binding fingerprint but may also be a key functional feature, associated with the altered photophysical behavior and lead to enhancement of excitation energy exchange with chlorophyll. 

The resonance Raman spectra are very rich in information. They carry not only a fingerprint of a type of carotenoid and its conformation, but also the information about molecular distortion. Even though the geometric changes are relatively small, resonance Raman can be very useful for the identification and the probing properties of the xanthophyll binding loci. 

The v4 region enhancement and structure in the resonance Raman spectra of xanthophylls reviewed in this chapter shows that it can be used for the analysis of carotenoid-protein interactions. Figure 7.8 summarizes the spectra for all four major types of LHCII xanthophylls. Lutein 2 possesses the most intense and well-resolved v4 bands. The spectrum for zeaxanthin is very similar to that of lutein with a slightly more complex structure. This similarity correlates with the structural similarity between these pigments. It is likely that they are both similarly distorted. The richer structure of zeaxanthin spectrum may be explained by the presence of the two flexible P-end rings... 

The use of selective isotope replacement of carbon and hydrogen atoms in the structure of xanthophylls in combination with LHCII reconstitution should greatly aid the assignment of multiple v4 twisting bands. This assignment would help localize the areas of distortion within the carotenoid molecule and understand the possible causes of this distortion. 

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