Fluorescence 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.)...

In PS I, as in PS II, there are a number of Chi alb protein complexes having lightharvesting and energy-transfer functions. Such complexes most probably exist in direct contact with the RC (part of the core complex), and certainly exist as peripheral LHC I antenna complexes further removed from the RC. A native PS I complex (80-180 Chi per RC, 100 kDa) with at least 6 polypeptides was isolated by solubilization of the thylakoid membrane with nonionic detergents (for example, Triton X-100) [177,178]. With further detergent treatment, the PS I complex dissociated into the core complex (CC I with the RC) and the peripheral antenna complex (LHC I) (spinach, barley, pea, Chlamydomonas reinhardtii [179-183]. The peripheral antenna complex (pea, spinach Chi alb ratio 4.0 1, typical fluorescence at 730 nm) contains 3-4 antenna polypeptides (19-25 kDa) [181,184,185]. This complex was also dissociated into two different antenna complexes - LHC la (2 polypeptides of 22 and 23 kDa) and LHC Ib (1 polypeptide, 20 kDa) - which differ in their fluorescence characteristics (680 nm and 730 nm) [184]. No structural data on these polypeptides are available at present. It was postulated that in C. reinhardtii, in addition to the peripheral antenna complex, an antenna system (with 4 polypeptides) exists, which connects the peripheral antenna energetically with the core complex CC 1 [183]. 

The above spectro-kinetic data obtained by time-resolved fluorescence measurements may thus be summarized with a model for pigment organization and excitation-energy transfer in the reaction center-antenna complex of green bacteria as follows ... 

H Van Amerongen, B Van Haeringen, M Van Gurp and R Van Grondelle (1991) Polarized fluorescence measurements on ordered photosynthetic antenna complexes chlorosomes of Chloroflexus aurantiacus and B800-850 antenna complexes of Rhodobacter sphaeroides. Biophys J 59 992-1001... 

Groot M-L, Peterman EJG, Van Stokkum IHM, Dekker JP and Van Grondelle R (1995) Triplet and fluorescing states ofthe CP47 antenna complex of Photosystem II studied as a function of temperature. Biophys J 68 281-290... 

D. Leupold, K. Teuchner, J. Ehlert, K-D. Irrgang, G. Renger, H. Lokstein, Two-photon excited fluorescence from higher electronic states of chlorophylls in photosynthetic antenna complexes A new approach to Detect strong excitonic chlorophyll a/b coupling, Biophys. J. 82, 1580-1585 (2002)... 

We have recently reported fluorescence from several carotenoids, including 3 Carotene, spheroidenone, spirilloxanthin and rhodopin(2). In this work we present new results on lycopene and spheroidene. Spheroidene has been chosen because it is the carotenoid in the B800-850 antenna complex of Rhodobacter spheroides, while lycopene due to its linear symmetric structure should be a good model for linear polyene. 

Fig. 1 Time-resolved fluorescence from Rb. capsulatus photosynthetic membranes lacking B800/850 antenna complexes. For each decay, an instrument response function is shown as well. (A) Weak measuring beam only. (B) Preillumination with a 532 nm pulse (about 3 mJ) about 50 ms before measurement.

The light-harvesting system of green bacteria consists of BChl c containing chlorosomes attached to the cell membrane by a baseplate containing BChl a. The cell membrane contains the B 808-866 antenna complex and the reaction center. We report here a comparison of the properties of chlorosome preparations obtained by different treatments. Energy transfer in these preparations was studied by picosecond absorbance recovery and steady-state fluorescence measurements. The results are used to propose a new model for the structure of chlorosomes. 

Results and Discussion. Figure 1 shows an example separation of Chlamydomonas chlorophyll-protein complexes solubilized with a mixture of octyl glucoside, decyl maltoside, and lithium dodecyl sulfate. The left hand panel shows the unstained green band pattern, while the right hand panel shows intrinsic room temperature chlorophyll fluorescence with excitation at 365 nm. This technique allows for the rapid assignment of antenna complexes, which fluoresce brightly, and reaction center complexes which are non-fluorescent or only weakly fluorescent at room temperature. 

As shown in Figure 3a, the cbn1-48 green band profile is substantially simplified relative to the wild type, with the complete or nearly complete loss of all chlorophyll b-containing antenna complexes. The non-fluorescent PSI bands all show an increase in electrophoretic mobility relative to the corresponding wild type bands, consistent with the loss of LHCl. The faintly fluorescent PSI I bands show an analagous increase in electrophoretic mobility,... 

De Caro C, Visschers RW, van Grondelle R and Volker S. Inter- and intraband energy transfer in LH2 antenna complexes of purple bacteria. A fluorescence line-narrowing and hole-burning study. J. Phys. Chem. 1994 98 10584-10590. 

Nagarajan, V., Parson, W. Femtosecond fluorescence depletion anisotropy application to the B850 antenna complex of Rhodobacter sphaeroides. J. Phys. Chem. B 104, 4010-4013 (2000)... 

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