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Studies on the reaction coordinates of the water oxidase in PS II membrane fragments from spinach
Author(s) -
Renger G.,
Hanssum B.
Publication year - 1992
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 - 10.1016/0014-5793(92)80092-u
Subject(s) - chemistry , spinach , reaction rate constant , redox , electron transfer , flash photolysis , crystallography , absorption (acoustics) , analytical chemistry (journal) , stereochemistry , kinetics , inorganic chemistry , physics , chromatography , biochemistry , quantum mechanics , acoustics
The temperature dependency of the rate constants of the univalent redox steps Y z ox S i → Y z S i+1 ( i = 0,1,2) and Y z ox S 3 → (Y z S 4 ) → Y z S o + O 2 in the water oxidase was investigated by measuring time resolved absorption changes at 355 nm induced by a laser flash train in dark adapted PS II membrane fragments from spinach. Activation energies of 5.0, 12.0 and 36.0 kJ/mol were obtained for the reactions Y z ox S i → Y z S i+1 with i = 0,1 and 2, respectively. The reaction Y z ox S 3 → (Y z S 4 ) → Y z S 0 + O 2 exhibits a temperature dependence with a characteristic break point at 279 K with activation energies of 20 kJ/mol ( T > 279 K) and 46 kJ/mol ( T > 279 K). Evaluation of the data within the framework of the classical Marcus theory of nonadiabatic electron transfer [(1985) Biochim. Biophys. Acta 811, 265–322] leads to the conclusion that the S 2 oxidation to S 3 is coupled with significant structural changes. Furthermore, the water oxidase in S 3 is inferred to attain two different conformational states with populations that markedly change at a characteristic transition temperature.