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Indirect evidence for structural changes coupled with Q −⋅ B formation in photosystem II
Author(s) -
Reifarth F,
Renger G
Publication year - 1998
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(98)00491-8
Subject(s) - photosystem ii , anoxygenic photosynthesis , chemistry , acceptor , analytical chemistry (journal) , quantum yield , fluorescence , crystallography , physics , photosynthesis , optics , chromatography , biochemistry , phototroph , condensed matter physics
The thermal blockage of Q −⋅ A oxidation was analysed in PS II membrane fragments by monitoring flash‐induced changes of the relative fluorescence quantum yield as a function of temperature. The results obtained reveal: (a) in dark‐adapted samples the fraction of Q −⋅ A that is not reoxidised within a time domain of 10 s after the actinic flash increases with lowering the temperature (half‐maximum effect at 250–260 K), (b) at low temperatures where Q −⋅ A generated in dark‐adapted samples remains almost completely reduced, a significant extent of Q −⋅ A reoxidation arises when samples are used that were preilluminated at room temperature by one saturating flash followed by rapid freezing before performing the experiment, and (c) the extent of Q −⋅ A that is reoxidised at 258 K exhibits a characteristic binary oscillation as a function of the number of preillumination flashes given at room temperature. Based on these data it is inferred that Q B and Q −⋅ B are located at different equilibrium positions in the Q B site. As a consequence the formation of Q −⋅ B is coupled with significant structural changes that require sufficient flexibility of the protein matrix. This general feature corresponds with a recently proposed model for the acceptor side reactions of anoxygenic bacteria [Stowell, M.H.B., McPhillips, T.M., Rees, D.C., Soltis, S.M., Abresch, E. and Feher, G., Science 276 (1997) 812–816].