The reactivity of hydrazine with photosystem II strongly depends on the redox state of the water oxidizing system

Abstract

The decay kinetics of the redox states SZ and & 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 NHrNHr a biphasic decay is observed. The rapid decline of 5% and S, with Yo as reductant exhibits practically the same kinetics with rm=67 s at pH=7.2 and 7°C. The slow reduction (order of 5-10 min at 7C) of S2 and S, with endogenous electron donors other than Yn is about twice as fast for S2 as for S, under these conditions. In contrast, the hydrazine-induced reductive shifts of the formal redox states S, (i = 0 3) are characterized by a totally different kinetic pattern: (a) at 1 mM NH2NH2 and incubation on ice the decay of S2 is estimated to be at least 25 times faster (t,,,<0.4 min) than the corresponding reaction of Sj E::;: E 13 min); (b) the NH?NHr-induced decay of S, is even slower (about twice) than the transformation of S, into the forma1 redox state 'S_,' ~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 NH2NH2-induced transformation So -+X2' [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,,2~2 min) than the reaction S, % 'S,'. Based on these results, the following dependence on the redox state S, of the reactivity towards NHzNHz is obtained: SA < S, < So 4 Sr. The implications of this surprising order of reactivity are discussed.

Absence of Mn-Centered Oxidation in the S2 → S3 Transition: Implications for the Mechanism of Photosynthetic Water Oxidation

“…Because this study does not provide an independent characterization of the S-state composition of their samples, this behavior can be explained if the actual miss parameter is significantly larger than the reported miss parameter of 9%. A high miss factor in this study could be caused by (a) the low energy per pulse of the laser, i.e., nonsaturating illumination, (b) the absence of exogenous electron acceptors, such as PPBQ, and (c) a significantly higher Y D content in the samples than the 25% that was assumed (up to 75% Y D has been observed 140,141 ). Furthermore, the pure S-state edge energies were determined by fitting the oscillation pattern of the half-height energies, not by deconvolution (or fitting) of the flash spectra.…”

Photosystem II: The machinery of photosynthetic water splitting

“…This finding supports earlier proposals on a significant structural change during the S 2 ? S 3 transition that were gathered from different lines of evidence (Boussac and Rutherford 1988;Messinger and Renger G 1990;Renger G and Hanssum 1992). New information on possible changes of Mn-Ca distances were obtained by EXAFS measurements on Sr 2?…”

Effects of methanol on the S i -state transitions in photosynthetic water-splitting

“…(ii) S 1 Y D ox thylakoids with Y D oxidized in about 90% of the centers were obtained by excitation of S 1 Y D samples (pH 6.0; 20°C) with one saturating flash and subsequent 5 min dark-incubation (Messinger and Renger 1990). …”