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Hydroxyl radical generation by photosystem II.
| Content Provider | Semantic Scholar |
|---|---|
| Author | Pospísil, Pavel Arató, András Krieger-Liszkay, Anja Rutherford, A. William |
| Copyright Year | 2004 |
| Abstract | The photogeneration of hydroxyl radicals (OH(*)) in photosystem II (PSII) membranes was studied using EPR spin-trapping spectroscopy. Two kinetically distinguishable phases in the formation of the spin trap-hydroxyl (POBN-OH) adduct EPR signal were observed: the first phase (t(1/2) = 7.5 min) and the second phase (t(1/2) = 30 min). The generation of OH(*) was found to be suppressed in the absence of the Mn-complex, but it was restored after readdition of an artificial electron donor (DPC). Hydroxyl radical generation was also lost in the absence of oxygen, whereas it was stimulated when the oxygen concentration was increased. The production of OH(*) during the first kinetic phase was sensitive to the presence of SOD, whereas catalase and EDTA diminished the production of OH(*) during the second kinetic phase. The POBN-OH adduct EPR signal during the first phase exhibits a similar pH-dependence as the ability to oxidize the non-heme iron, as monitored by the Fe(3+) (g = 8) EPR signal: both EPR signals gradually decreased as the pH value was lowered below pH 6.5 and were absent at pH 5. Sodium formate decreases the production of OH(*) in intact and Mn-deleted PSII membranes. Upon illumination of PSII membranes, both superoxide, as measured by EPR signal from the spin trap-superoxide (EMPO-OOH) adduct, and H(2)O(2), measured colormetrically, were generated. These results indicated that OH(*) is produced on the electron acceptor side of PSII by two different routes, (1) O(2)(*)(-), which is generated by oxygen reduction on the acceptor side of PSII, interacts with a PSII metal center, probably the non-heme iron, to form an iron-peroxide species that is further reduced to OH(*) by an electron from PSII, presumably via Q(A)(-), and (2) O(2)(*)(-) dismutates to form free H(2)O(2) that is then reduced to OH(*) via the Fenton reaction in the presence of metal ions, the most likely being Mn(2+) and Fe(2+) released from photodamaged PSII. The two different routes of OH(*) generation are discussed in the context of photoinhibition. |
| Starting Page | 1 |
| Ending Page | 2 |
| Page Count | 2 |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.psi.cz/ftp/publications/papers/pdf/Pospisil_2004.pdf |
| PubMed reference number | 15157112v1 |
| Volume Number | 43 |
| Issue Number | 21 |
| Journal | Biochemistry |
| Language | English |
| Access Restriction | Open |
| Subject Keyword | 8a-hydroperoxy-tocopherone CATALASE Edetic Acid Exhibits as Topic Formates Heme Iron Hydroxyl Radical Ions Kinetics Manganese Oxidants Oxygen Peroxides Photosystem II Superoxide Dismutase Superoxides Tissue membrane adduct formic acid, sodium salt photoinhibition |
| Content Type | Text |
| Resource Type | Article |
