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The reactivity of hydrazine with photosystem II strongly depends on the redox state of the water oxidizing system
Author(s) -
Messinger J.,
Renger G.
Publication year - 1990
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(90)80829-8
Subject(s) - chemistry , redox , oxidizing agent , spinach , photosystem ii , thylakoid , yield (engineering) , kinetics , dcmu , reactivity (psychology) , photochemistry , medicinal chemistry , inorganic chemistry , photosynthesis , chloroplast , biochemistry , thermodynamics , organic chemistry , medicine , physics , alternative medicine , quantum mechanics , pathology , gene
The decay kinetics of the redox states S 2 and S 3 of the water‐oxidizing enzyme have been analyzed in isolated spinach thylakoids in the absence and presence of the exogenous reductant hydrazine. In control samples without NH 2 NH 2 a biphasic decay is observed. The rapid decline of S 2 and S 3 with y D as reductant exhibits practically the same kinetics with t 1/2 = 6‐7 s at pH = 7.2 and 7°C. The slow reduction (order of 5‐10 min at 7°C) of S 2 and S 3 with endogenous electron donors other than y D is about twice as fast for S 2 as for S 3 under these conditions. In contrast, the hydrazine‐induced reductive shifts of the formal redox states S i (i = 0⋯3) are characterized by a totally different kinetic pattern: (a) at 1 mMNH 2 NH 2 and incubation on ice the decay of S 2 is estimated to be at least 25 times faster ( t 1/2 ⩽0.4 min) than the corresponding reaction of S 3 ( t 1/2 ≈13 min); (b) the NH 2 NH 2 ‐induced decay of S 2 is even slower (about twice) than the transformation of S 1 into the formal redox state ‘S −1 ’ ( t 1/2 ≈6 min), which gives rise to the two‐digit phase shift of the oxygen‐yield pattern induced by a flash train in dark adapted thylakoids. (c) the NH 2 NH 2 ‐induced transformation S 0 →‘S −2 ’ [Renger, Messinger and Hanssum (1990) in: Curr. Res. Photosynth. (Baltscheffsky, M., ed). Vol. 1, pp. 845‐848, Kluwer, Dordrecht] is about three times faster ( t 1/2 ≈ min) than the reaction. Based on these results, the following dependence on the redox state S i of the reactivity towards NH 2 NH 2 is obtained: S 3 < S 1 < S 0 ⪡ S 2 . The implications of this surprising order of reactivity are discussed.