Chlorophyll-carotenoid-protein complexe

Takahashi, Y., Hirota, K., and Katoh, S., Multiple forms of Pygo Chlorophyll a-protein complexes from Synechococcus sp. PCC 6803 The hon, quinone, and carotenoid contents, Photosynth. Res., 6, 183,1985. 

The protein complex of T. elongatus consists of 12 subunits that contain 96 Chi a and 22 carotenoid molecules, 3 [4Fe4S] centres and 2 phylloquinone (vitamin K,) molecules (for molecular structures see Fig. 2). The cofactors of the ET chain are arranged in two branches as pairs of molecules related by a pseudo-C2 axis. After light excitation an electron is donated from the primary donor P700, a pair of chlorophylls, to monomeric chlorophyll a (acceptor A0), phylloquinone (A() and the 3 iron-sulfur centres (F , Oa and B). It has been controversially discussed in the literature whether both highly symmetric pigment branches are... 

Carotenoids involved in photosynthesis are bound to and help stabilize chlorophyll-protein complexes, of which various types occur in the lamellar membranes of chloroplasts (Fig. 1-10). Carotenoids also are found in organelles known as chromoplasts, which are about the size of chloroplasts and are often derived from them. For instance, lycopene (red) is in tomato fruit chromoplasts, and a- and pi-carotenes (orange) occur in carrot root chromoplasts. A great diversity of carotenoids occurs in the chromoplasts of flower petals, which is important for attracting pollinators, and fruits, which aids in seed dispersal by attracting other animals. 

Figure 3. Fiincvional organisation oFpholosyslem I (in protein complexes contained in the thylakoid membrane. Excitation energy is harvested by chlorophyll (Chi) and carotenoids (Car) molecules and transfered to the special pair (Chlj). Vectorial electron transfer across the membrane takes place front excited Chi to plastoqutnone (pQ) via phcopliitin (Ph) and quinone (Q) electron mediators.

Although all chlorophyll-protein complexes isolated to date, whether they are associated with PS I or II, contain carotenoids, it is only in two classes of complexes that carotenoids play the major light-harvesting role. These two classes are the unique... 

Akimoto S, Takaichi S, Ogata T, Nishinura Y, Yamazaki I and Mimuro M (1996) Excitation transferin carotenoid-chlorophyll protein complexes probed by femtosecond fluorescence decays Chem Phys Lett 260 147-152... 

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