Part III - Optical Rotatory Dispersion of Chlorophyll-Containing Particles from Green Plants and Photosynthetic Bacteria

Abstract

This chapter presents the optical rotatory dispersion (ORD) of chlorophyll-containing particles from green plants and photosynthetic bacteria. The ORD spectra of chlorophylls a and b in diethyl ether in the visible and near-ultraviolet regions were first measured using a sensitive spectropolarimeter. ORD spectra of chloroplast-lamellae fragments, which represent chlorophyll bound to the lipoprotein in the native state, were reported. The ORD spectrum of the chlorophyll-lipoprotein shows considerably more complexity and intensity than that of free chlorophylls (a + b) at the same concentration in an organic solvent. Cotton effects corresponding to almost all the absorption bands of Chl a and Chl b are retained in the lipoprotein complex. Heating a chloroplast preparation presumably causes denaturation of enzyme proteins and disruption of the organizational relationship between the pigment and the lipoprotein. Structural changes of this sort are not readily revealed by absorption spectra. ORD spectra of the chlorophyll-containing particles from several photosynthetic bacteria were also reported. Cotton effects associated with the carotenoids can be clearly seen, as, unlike in chloroplasts, the absorption regions of Bchl and the carotenoids are well separated. The enhancement of the intrinsic Cotton effects of the chlorophylls and carotenoids that are complexed with the lipoprotein suggests a strong interaction either between the pigment molecules themselves or between the pigment molecules and the attached lipoprotein macro-molecules. A more definite theoretical interpretation of the relationship between the electronic transition of the bound pigment moieties and the observed Cotton effects still remains to be worked out.