Electron Acceptors in Photosystem II
Several components have been identified on the acceptor side of PSII including I (pheophytin), QA and QB (plastoquinones). However a number of experiments including fluorescence spectroscopy1 and E.P.R.2 suggest that the acceptor side is very complex and that additional electron acceptors may exist. We have used absorption spectroscopy to study the acceptor side of photosystem II by following the reduction of the P680 cation formed by a laser flash. In samples where oxygen evolution is active almost all P680 is reduced by various components on the donor side, this takes place in <50ns, faster than the response time of our spectrophotometer. Treatment with hydroxylamine plus illumination inhibits oxygen evolution and electron donation from the donor D. P680+ is now reduced more slowly (µs & ms) by back reactions from reduced electron acceptors formed by the reaction P680+ hv> P680+ + e-.
KeywordsElectron Acceptor Oxygen Evolution Laser Flash Acceptor Side Donor Side
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- 5.P.L. Dutton, Redox Potentiometry, in: Methods in Enzymology, Vol.54, Academic Press, 411 (1978).Google Scholar