| PSI is important to the whole photosynthesis. The structure and function of PSI are studied in this paper. First, the PSI particles were extracted from spinach leaves and its degradation and deactivation were analyzed in order to study the effects of heat treatment. Secondly, greening experiment was designed and thylakoid membranes were extracted from Chlamydomonas reinhardtii y-1 cells in order to study the changes of PSI core complex (CPI). In addition, the membrane lipids and its fatty acids in Chlamydomonas reinhardtii y-1 cells were analyzed to determine their synthesis and transfer mechanism occurred during the greening stage.I . The effects of high temperature treatment (25℃ ~80℃) on structure and function of PSI was characterized by spectroscopy, oxygen electrode polarography, SDS-PAGE. The main results were summarized as followings:1. During linear heating, the absorption maximum at 680 nm of PSI decreased and blue-shifted, of which pigments and polypeptides in PSI complexes degraded at high temperature. The chlorophyll a (Chl a) molecules with maximum absorption at 683 nm in the fourth derivative absorption spectra, which are mainly attributed to light harvesting complex of PSI (LHCI), were more sensitive to high temperature. So it was suggested that Chl a (absorbing at 683 nm) was destroyed firstly by elevated temperature.2. The characteristic peak at 728 nm and the ratio of F728-F720 to F680 in 77K fluorescence spectra decreased apparently when temperature increased, showing that high temperature blocked energy transfer in LHCI and the energy transfer from LHCI 680 to LHCI 730 and PSI reaction center was inhibited.3. SDS-PAGE displayed that PsaA/B subunits and LHCI subunits were degraded and aggregated at different levels upon linear heat treatment.However, at high temperature especially at 90℃~100℃, the PsaA/B subunits disappeared completely while LHCI subunits remained, indicating that the core complex subunits were more sensitive to heat treatment than LHCI subunits.4. The probable mechanism based on the above results is that during linear heating the disconnection of the antenna from the reaction center occurred and then followed by the inhibition of the photochemical charge separation in reaction center.5. Quantitative analysis of the component bands in the amide I band (1700-1600 cm-1) showed that no significant change occurred below 50℃. However, apparent conformational changes occurred at 60℃ and were further continued at 70 and 80℃ accompanied with transitions of secondary structure mainly from a-helix to the 6-sheet structures.6. CD analysis demonstrated that the regular arrangement viz. protein microenvironment of pigments of PSI complexes was destroyed by heat treatment, which maybe come from the changes of protein secondary structure of PSI. It can be found that the CD signals at 645 nm contributed Chlb (chlorophyll b) of light-harvesting complex I (LHCI) was easy to be destroyed at the beginning of heat treatment (25-60℃); when temperature reached 70 and 80℃, the CD signals at 478 nm contributed mainly by Chlb of LHCI and 498 nm contributed by Carotenoids were decreased most rapidly, indicating that LHCI was more sensitive to high temperature than core complexes.7. The oxygen uptake rate decreased with the increase of temperature, and was almost completely lost at around 70℃, demonstrating that the PSI complexes were destroyed seriously when the temperature reached 70℃. This probably attributed to heat-induced changes of pigment microenvironment and protein secondary structure especially transmembrane a-helix located in PsaA/B of PSI.II . With Green gel electrophoresis and western blotting, Chlorophyll apoproteins and chlorophyll-protein complexes in CPI were examined in degreened cells of Chlamydomonas reinhardtii y-1 by growth in the dark for 4 days.In the dark, CPI, was absent. But the core polypeptides PsaA/B were existed clearly. At the same time, P700 was not detected in dark-grown cells. When the etiolated c...
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