Reaction centre photosystem

Kranss, N., et al., 1996. Photosystem I at 4 A resolution represents the first structural model of a joint photosynthedc reaction centre and core antenna system. Nature Structural Biology 3 965-973. 

A, Absorption chi, chlorophyll car, carotenoid EET, excitonic energy transfer EF, exoplasmic fracture face EM, electron microscopy FWHM, full width at half maximum lEF, Isoelectric Focusing, LD, linear dichroism LHC, light harvesting complex PAGE, polyacrylamide gel electophoresis PF, protoplasmic fracture face PS, photosystem RC, reaction centre SDS, sodium dodecyl sulphate SSTT, single step transfer time. 

Fig. 5. Light-induced formation and dark decay of P7001 in the reaction centre of the photosystem 1 of subchloroplasts at T < 294 K [45], The arrows indicate the moments of switching the light on ( ) and off (t).

Fig. 7. Temperature dependence [45] of the rate constant of decay of P700+ in the reaction centre of photosystem 1 of subchloroplasts at T 240 K.

Thus, the study [45] of the kinetics of the charge recombination in the reaction centres of photosystem 1 of subchloroplasts over wide time and temperature intervals has shown an essential difference in the kinetics of the tunneling decay of P700+ at high and low temperatures. The quantitative description of the electron transfer kinetics has proved possible in terms of the assumption of a difference in charge recombination rate constants for different reaction centres. Such a difference may be due, for example, to a non-coincidence, for different reaction centres, of electron tunneling distances or to different conformational states of these centres. 

Fig. 3 Schematic model of light-harvesting compartments in photosynthetic organisms and their position with respect to the membrane and the reaction centers. RC1(2) Photosystem I(II) reaction centre. Peripheral membrane antennas Chlorosome/FMO in green sulfur and nonsulfur bacteria, phycobilisome (PBS) in cyanobacteria and rhodophytes and peridinin-chlorophyll proteins (PCP) in dyno-phytes. Integral membrane accessory antennas LH2 in purple bacteria, LHC family in all eukaryotes. Integral membrane core antennas B808-867 complex in green nonsulfur bacteria, LH1 in purple bacteria, CP43/CP47 (not shown) in cyanobacteria and all eukaryotes.

Recombination of Charges in the Reaction Centres of the Photosystem 1 of Plants... 

Fig. 28. Dark decay [212] of P700+ in the reaction centre of photosystem 1 of subchloroplasts at T < 240 K (a) and at T St 240 K (b). Proposed schematic structures of the reaction centre at low and high temperatures are shown at the bottom of the Fig. (c)...

Thus, the study [212, 214] of the kinetics of the charge recombination in the reaction centres of photosystem 1 of subchloroplasts over wide time and temperature intervals has shown an essential difference in the kinetics of the tunneling... 

Takahashi, Y., Hansson, O., Mathis, P. and Satoh, K. 1987. Primary radical pair in the Photosystem II reaction centre. Biochim. Biophys. Acta, 893. 49-59. 

Williams-Smith, D.L., Heathcote, P., Sihra, C.K. and Evans, M.C.W. 1978. Quantitative EPR measurements of the electron-transfer components of the photosystem I reaction centre. Biochem. J., 170. 365-371. 

The present paper summarises our recent results relating to the location and structure of the reaction centres of photosystems I and II, with particular reference to the organisation of the chlorophyll-proteins and the transfer of excitation energy from antennae to the reaction centres. 

The exclusive localisation of photosystem I in stroma lamellae was demonstrated directly by immunogold labelling of isolated thylakoids (Vallon et al. 1985, 1986, 1987b). Monoclonal antibodies raised against the barley photosystem I reaction centre (P700 Chla-Pl or CPI) are incubated with thin sections of wild type... 

Photosystem II reaction centres have been shown to be located mainly in the appressed granal membranes by a number of independent but indirect methods, including thylakoid fractionation, de-stacking and re-stacking experiments and chemical modification. Further evidence has come from freeze-fracture investigations of mutants specifically deficient in photosystem II in barley (Simpson et al., 1977), tobacco (Miller and Cushman, 1979) and Chlamydomonas (Olive etal. 1979). In all cases, there was a partial or almost... 

In contrast to LHCI, the light-harvesting chlorophyll a/b-antennae complex of photosystem II (LHCII) is the major component of the particles on the complementary protoplasmic fracture face of appressed membranes (PFs) (Simpson, 1979, Olive et al., 1979), and does not appear to be a significant component of the reaction centre EFs particles, although this is disputed. The LHCII in PFs particles is, nevertheless, in contact with the reaction centre particles and may provide a pathway for excitation energy transfer between several photosystem II reaction centres. 

FIGURE 4. Freeze-fracture electron micrographs of thylakoids from (a) wild type, (b) the photosystem II mutant viridis —115 and (c) the chlorophyll b-less mutant chlorina-f2. The EFs particles found in the wild type (a) are almost all missing from the photosystem II mutant (b), indicating that the photosystem II reaction centre is located in these particles. The PFs particles are missing from the chlorophyll b-less mutant (c), showing that LHCII, the major chlorophyll-containing protein is the major constituent of the PFs particles in wild type thylakoids. 

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