Chlorophyl antenna system

Neoxanthin and the two lutein molecules have close associations with three transmembrane helixes, A, B, and C, forming three chlorophyll-xanthophyll-protein domains (Figure 7.5). Considering the structure of LHCII complex in terms of domains is useful for understanding how the antenna system works, and the functions of the different xanthophylls. Biochemical evidence suggests that these xanthophylls have a much stronger affinity of binding to LHCII in comparison to violaxanthin... 

The amount of 02 released when a suspension of algae (Chlorella pyrenoidosa) was excited with a train of short flashes of light, as a function of (a) the time between the flashes and (b) the intensity of the flashes. Each flash lasted about 10 /as. The total amount of 02 released was measured after several thousand flashes and was divided by the number of flashes and by the amount of chlorophyll in the suspension. (What happens on the first few flashes is discussed later.) The measurements in (a) were made with flashes comparable to the strongest flashes used in (b). For the measurements shown in (b), the flashes were spaced 20 ms apart. Note that the maximum amount of 02 released per flash was only one molecule of 02 per several thousand molecules of chlorophyll. With saturating flashes, the amount of 02 evolution is limited by the concentration of reaction centers, whereas most of the chlorophyll in the algae is part of the antenna system. 

Bassi, R., Hover-I I an sen G., Barbato R., Giacometti G.M. and Simpson D.J. 1987. Chlorophyll-proteins of the photosystem II antennae system. J. Biol. Chem. 262, in press. 

Figure 2.19. Molecular configurations of chlorophyll-a (C5jH72N405Mg), pheophytin (C55H74N4O5) and tyrosine (C9H11NO3). For clarity the detailed three-dimensional structure is not followed in detail. The surrounding environment would influence it. The tail components of the chlorophyll and pheophytin molecules serve to stabilise the placement of the molecules in the thylakoid membrane. Chlorophyll-b, a kind found among the chlorophylls of the antenna system in some photosystems, differs from chi a by having one CH3 group replaced by CHO.

Schiller, H., Senger, H., Miyashita, H., Miyachi, S. and Dau, H. Light-harvesting in Acaryochloris marina — spectroscopic characterization of a chlorophyll -dominated photosynthetic antenna system. FEBS Letters 410 433-436 1997. 

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