Without Photosystem

Some plant HSPs are known to be associated with chloroplasts. Although chloroplasts and mitochondria do not synthesise HSP themselves (Nieto-Sotelo Ho, 1987), certain nuclear encoded HSPs synthesised in the cytosol have been shown to be transported into chloroplasts (Kloppstech et al., 1985 Vierling et al., 1986). The HSP22 of Chlamydomonas is incorporated into the thylakoid membrane without size reduction, while in pea, HSP22 is synthesised as a 26 kDa precursor. In Chlamydomonas, Schuster et al. (1988) have shown that the HSP22 is associated with the photosystem... 

Another method used to vary the AG° of the recombination reaction without chemical modification of the centers, consists of placing the system in an electric field whose orientation and intensity are well defined [141]. However, the energy level shifts induced by the field also change the electronic factors, so that the interpretation of the experimental results is not straightforward. Bixon and Jortner have proposed using electric field effects to elucidate the nature of the primary electron step in bacterial photosystems [142], a problem that will be discussed in Sect. 3.5. One basic difficulty encountered in this method is the evaluation of the internal field effectively seen by the redox centers in the membrane. 

A relatively simple and quick procedure for the isolation of Photosystem I-enriched particles from the thermophilic cyanobacterium Phormidium laminosum, without the use of detergents for solubilization, is described. The procedure involves sonication of cells, centrifugation and DEAE-cellulose chromatography. The particles had an 02 uptake activity of up to 200 pmol 02. mg chlorophyll h 1 and appeared as vesicles of 200 100 nm diameter when observed under electron microscopy. The analysis of the chlorophyll-protein complexes by polyacrylamide gel electrophoresis showed that these particles are enriched in the complexes associated with Photosystem I and partially depleted in those associated with Photosystem II. The particles did not contain ferredoxin and were active in NADP-photoreduction only in the presence of added ferredox in. They were also able to photoreduce externally added electron mediators using ascorbate as electron donor, the reduced mediators can be coupled to hydrogenase for the production of H2 or for the activation of cyanobacterial phosphoribulokinase using a ferredoxin/thioredoxin system. 

The bacterial photosystem functions without dioxygen production which simplifies the task at hand. Namely, electrons are obtained from more easily oxidized terminal electron donors such as H2S instead of water. Nonetheless, the basic design needed to transform solar energy into stored chemical energy is present. The protein subunits and cofactors that comprise the photosystem in purple bacteria, such as Rhodobacter (Rb.) sphaeroides and Rhodopseudomonas (Rps.) viridis,33 are shown schematically in Fig. 1 which is based on a crystal structure of this assembly.34... 

As already stressed, photosystem II herbicides bind reversibly to their binding site. A1tough radiolabeled herbicides are available, it is impossible to identify the herbicide receptor protein without a chemical modification of the herbicide that allows for covalent... 

Fig. 2. (A) Flash-induced AA in the SDS-fractionated PS-1 core complex (CPI) at 5 K [ with and o without DCIP] (B) Flash-induced AA in TSF-I particles containing dithionite and neutral red at pH 10 and frozen while being illuminated (C) left AA induced by 300-ns, dye laser flashes [710 nm for the blue and green region 590 nm for the red region] insets show individual AA transients at 696 and 480 nm (C) right The difference between the difference spectrum in the left panel and that of P700. (D) Plot of the rate constant vs. reciprocal temperature. Figure source (A) Mathis, Sauer and Remy (1978) Rapidly reversible flash-induced electron transfer on a P-700 chlorophyll-protein complex isolated with SDS. FEBS Lett 88 277 (8) Sauer, Mathis, Acker and van Best (1979) Absorption changes of P-700 reversible in milliseconds at low temperature in Triion-solubilized photosystem I particles. Biochim Biophys Acta 545 469 (C and D) Shuvalov, Dolan and Ke (1979) Spectral and kinetic evidence for two eariy electron acceptors in phoiosystem I. Proc Nat Acad Sci, USA 76 771,773.

Hg. 6. Laser flash-induced absorbance changes (AA) observed in a core complex at 819 nm (A) and 380 nm (B) at 298 K aA at 819 nm presented on three time scales with parameters derived by computer cun/e fitting AA at 380 nm without and with ferricyanide (C) absorbance difference spectra in the UV/vis region constructed from the 10-//s- and 100-ps decay phases. Figure source Brettel and Golbeck (1995) Spectral and kinetic characterization of electron acceptor A, in a photosystem I core devoid of iron-sulfur centers Fx, Fb and Fa- Photosynthesis Res 45 185,187. 

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