| Abstract |
The interaction of the extrinsic with the intrinsic proteins of the Photosystem II core-complex and their relationship with the inorganic cofactors of PS II is under contention. Solubilization of Photosystem II (PS II) membrαnes with the non ionic detergent 6-O-(N-heptacarbamoyl)-methyl-a-D-glucopyranoside (HECAMEG) allowed the isolation of an oxygen evolving PS II-core complex, which retains the 23 and 17 kDa extrinsic polypeptides. The pattern of proton release as a function of flash number in this PS II complex, which retains all three extrinsic proteins, was found to be close to 1:1:1:1, during the S-state cycle. Previous studies had shown the same pattern, but in core-complexes that had not the 23 and 17 kDa proteins. Thus, the presence of 23 and 17 kDa polypeptides does not change the pattern of proton release. Mild trypsinization of the PS II complex resulted in proteolysis of D1 protein, while all three extrinsic proteins (33,23 and 17 kDa) and the manganese complex remained intact: under these conditions the pattern of proton release remained closed to 1:1:1:1. Although both the donor and acceptor side seem to remain intact after the mild trypsinization, the oxygen evolution activity decreases to 65% compairing to the control core complex. Similar results were obtained with PS II-core complexes, that had been isolated using other detergents. In order to expalain the decrease of oxygen evolution activity, mild trypsinization took place at room temperature. Temperature sensitivity was observed, as the oxygen evolution activity was almost lost, while the manganese content remained intact. The investigation of the interaction of the extrinsic with the intrinsic proteins of the Photosystem II-core complex was also examined, by using chemical substances, which can cross-link some of the proteins. EDC [1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide] is a zero-length cross-linker, which modifies carboxyl groups and cross-links amino groups to carboxyl groups, that are in van der Waals contact. It has been suggested that EDC cross-links the 33 kDa protein with the CP 47. Further examination of the protein cross-linking using EDC, showed that the 23 kDa protein cross-links with the a-subunit of cyt b559, but couldn't give enough information about the interaction of the 33 kDa protein with the 23 and 17 kDa polypeptides. Finally, in order to examine the influence of the ionic strength to the extrinsic proteins and if NO2- competes with the Cl- ions, LiClO4 and KNO2 were used, respectively. It has been found that treatment of PS II membranes with 100mM LiClO4 resulted in 23 and 17 kDa proteins release, while with 500mM LiClO4, 33 kDa protein was also released. Treatment of PS II membranes with KNO2 resulted in slower electron transport from QA to QB, explaining the decrease of oxygen evolution activity that was observed after the treatment, without affecting the extrinsic polypeptides 33,23 and 17 kDa . Finally, in order to examine the influence of the ionic strength to the extrinsic proteins and if NO2- competes with the Cl- ions, LiClO4 and KNO2 were used, respectively. It has been found that treatment of PS II membranes with 100mM LiClO4 resulted in 23 and 17 kDa proteins release, while with 500mM LiClO4, 33 kDa protein was also released. Treatment of PS II membranes with KNO2 resulted in slower electron transport from QA to QB, explaining the decrease of oxygen evolution activity that was observed after the treatment, without affecting the extrinsic polypeptides 33,23 and 17 kDa .
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Μελέτη του ρόλου των πρωτεϊνών του πυρήνα του φωτοσυστήματος II
