Antenna chlorophyll system

Such a process can naturally be expected to play a certain part in the mechanism of directed energy transport in biological systems, in particular, in the transfer of absorbed energy from the antenna chlorophyll molecules to the reactive center in the photosynthetic system of plants. In Ref. [30], energy exchange between molecules of the photosynthetic pigments chlorophyll a and pheophytin a was studied experimentally with pigments introduced into the polar matrix. 

Reaction (14) and hence the overall rate of electron phototransfer across the membrane can be enhanced by providing additional excitation of the ZnTPPin molecules on the inner membrane surface. It could be done by virtue of energy transfer from some antenna collecting light and then transferring the excitation to the reaction centers , i.e. the ZnTPPin molecules embedded into the membrane this approach reproduces the action of a pull of the antenna chlorophyll in chloroplasts. In corresponding experiments (System 14 of Table 1) a water-soluble... 

Photosystems-I thylakoids of higher plants and cyanobacteria are quite different from the bacterial system in that, for instance, besides having peripheral chlorophyll-protein complexes as antenna, there are also chlorophyll molecules functioning as the so-called core antenna complex in the reaction-center itself. A PS-1 core complex containing core antenna chlorophyll molecules was actually obtained as early... 

The first cyclic porphyrin dimer (cyclophane porphyrin) linked with two ester groups 15 was synthesized as a model of antenna chlorophyll dimer by condensation of a 2,12-dipropionate porphyrin and a 2,12-bis-(3-hydroxypropyl) porphyrin in high dilution in 1977." In order to clarify the mechanism of electron-transfer reactions in biological systems, a variety of porphyrin dimers have been reported as model systems of parts of the photosynthetic apparatus in the last two decades. The first synthesis of cyclic porphyrin oligomers was reported by Hamilton, Lehn and Sessler in 1986. ... 

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 analysis of carotenoid identity, conformation, and binding in vivo should allow further progress to be made in understanding of the functions of these pigments in the photosynthetic machinery. One of the obvious steps toward improvement could be the use of continuously tuneable laser systems in order to obtain more detailed resonance Raman excitation profiles (Sashima et al 2000). This technique will be suitable for the investigation of in vivo systems with more complex carotenoid composition. In addition, this method may be applied for the determination of the energy of forbidden Sj or 2 Ag transition. This is an important parameter, since it allows an assessment of the energy transfer relationship between the carotenoids and chlorophylls within the antenna complex. 

Of all the systems where Forster dipole—dipole energy transfer has been identified, the most important is light harvesting by antennae chloro-phyll-b molecules and donation of singlet energy to the chlorophyll-a reaction centres in photosynthetic organisms. Typical values of R0 have been estimated to be 4—5nm. Further details of photosynthesis may be found in articles by Birks [6, 141,142], Berlman [127], Gregory [144], and Jortner [145]. 

The structure of the core antenna of Photosystem I (PSI) stands in striking contrast to the bacterial system. The 96 non-equivalent chlorophyll (Chi) molecules are very densely... 

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. 

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