Absorption antenna complex

Figure 10.16 Solar energy transfer from accessory pigments to the reaction centre, (a) The photon absorption by a component of the antenna complex transfers to a reaction centre chlorophyll, or, less frequently, is reemitted as fluorescence, (b) The electron ends up on the reaction centre chlorophyll because its lowest excited state has a lower energy than that of the other antenna pigment molecules. (From Voet and Voet, 2004. Reproduced with permission from John Wiley Sons., Inc.)...

The carotenoid absorption band of each purified preparation of antenna complexes was similar, in shape and location, to that of the membranes from which that particular preparation was derived. Besides, the similitude was kept unchanged after organic solvent extraction of the preparations (not shown). Then, it seems that the incorporation of carotenoid pigments to the antenna complexes in vivo is a nonspecific process. The detection of spirilloxanthin as the sole carotenoid of previously analyzed antenna preparations of the same microorganism seems to be accidental and, as suggested by Duysens (in Cogdell and Thomber, 1979, pp. 77), probably due to the use of old, spirilloxanthin enriched cultures as the starting material for complex solubilization. 

The well-ordered pigment clusters of the antenna complexes having different absorption maxima are the basis of heterogeneous, directed energy transfer between the antenna complexes to the RC (Fig. 1C). 

Fig. 2. Spectral range (absorption in nm) of the antenna system of oxygenic (plants, algae, cyanobacteria) and anoxygenic (green and purple bacteria) photosynthetic organisms. The antenna systems (antenna complexes) are located either within (intramembrane) or on the surface (extramembrane) of the photosynthetic membrane.

H.-M. Wu, M. Ratsep, R. Jankowiak, R.J. Cogdell, G.J. Small, Hole burning and absorption studies of the LHl antenna complex of purple bacteria Effects of pressure and temperature. J. Phys. Chem. B 102, 4023-4034 (1998)... 

Since the bacteriochlorophyll present in the light-harvesting complex accounts for the majority of all the bacterial pigments, its absorption bands can readily be identified even in the spectrum of the unfractionated membrane. On the other hand, the pigments belonging to the reaction center amount to only "1% of the total BChl and its absorption is often masked by the bulk pigments. The BChl a present in the reaction center may be identified however in a purified reaction-center preparation isolated from the chromatophore membrane. This may be illustrated with Chromatium vinosum following fractionation and isolation of the reaction-center complex and the three antenna complexes from the chromatophore membrane. Fig. 2 (B) shows the absorption spectrum of the unfractionated Chromatium chro-... 

The baseplate is about 5 nm thick and contains a particular BChl a-protein complex, namely B795 (see Fig. 4 below). Here B stand for the word bulk, as in Chapter 3 where reference is made to lightharvesting BChl-proteins, and the number refers to the wavelength of the major absorption bands of the complex in the far-red. The B795-complex serves as an intermediate for transfer of electronic excitation energy from the chlorosome to components in the cytoplasmic membrane. The core complex in the cytoplasmic membrane consists of small core antenna complexes, B806-866, and the reaction-center complex (P865 in Chloroflexaceae sp.). 

The photosystems responsible for absorption of light energy are composed of two linked components, the reaction center and an antenna complex. What is the pigment composition and role of each in the process of light absorption What evidence exists that the pigments found in these components are Involved in photosynthesis ... 

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