Journal ArticleDOI
pH-Dependent charge equilibria between tyrosine-D and the S states in photosystem II. Estimation of relative midpoint redox potentials
Imre Vass,Stenbjoern Styring +1 more
TLDR
It is proposed that this monoprotic event reflecting the protonation of an amino acid residue, probably histidine-190 on the D2 protein, to which YD is hydrogen bonded, affects the water-oxidizing complex.Abstract:
The effect of protonation events on the charge equilibrium between tyrosine-D and the water-oxidizing complex in photosystem II has been studied by time-resolved measurements of the EPR signal IIslow at room temperature. The flash-induced oxidation of YD by the water-oxidizing complex in the S2 state is a monophasic process above pH 6.5 and biphasic at lower pHs, showing a slow and a fast phase. The half-time of the slow phase increases from about 1 s at pH 8.0 to about 20 s at pH 5.0, whereas the half-time of the fast phase is pH independent (0.4-1 s). The dark reduction of YD+ was followed by measuring the decay of signal IIslow at room temperature. YD+ decays in a biphasic way on the tens of minutes to hours time scale. The minutes phase is due to the electron transfer to YD+ from the S0 state of the water-oxidizing complex. The half-time of this process increases from about 5 min at pH 8.0 to 40 min at pH 4.5. The hours phase of YD+ has a constant half-time of about 500 min between pH 4.7 and 7.2, which abruptly decreases above pH 7.2 and below pH 4.7. This phase reflects the reduction of YD+ either from the medium or by an unidentified redox component of PSII in those centers that are in the S1 state. The titration curve of the half-times for the oxidation of YD reveals a proton binding with a pK around 7.3-7.5 that retards the electron transfer from YD to the water-oxidizing complex. We propose that this monoprotic event reflects the protonation of an amino acid residue, probably histidine-190 on the D2 protein, to which YD is hydrogen bonded. The titration curves for the oxidation of YD and for the reduction of YD+ show a second proton binding with pK approximately 5.8-6.0 that accelerates the electron transfer from YD to the water-oxidizing complex and retards the process in the opposite direction. This protonation most probably affects the water-oxidizing complex. From the measured kinetic parameters, the lowest limits for the equilibrium constants between the S0YD+ and the S1YD as well as between the S1YD+ and S2YD states were estimated to be 5 and 750-1000, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)read more
Citations
More filters
Journal ArticleDOI
Water-splitting chemistry of photosystem II.
James P. McEvoy,Gary W. Brudvig +1 more
TL;DR: Life on earth is almost entirely solar-powered, with carbohydrate acting as a source of high-energy electrons and dioxygen providing a lower-energy destination for these electrons.
Journal ArticleDOI
The manganese and calcium ions of photosynthetic oxygen evolution.
Journal ArticleDOI
Manganese Compounds as Water-Oxidizing Catalysts: From the Natural Water-Oxidizing Complex to Nanosized Manganese Oxide Structures
Mohammad Mahdi Najafpour,Gernot Renger,Małgorzata Hołyńska,Atefeh Nemati Moghaddam,Eva-Mari Aro,Robert Carpentier,Hiroshi Nishihara,Julian J. Eaton-Rye,Jian Ren Shen,Jian Ren Shen,Suleyman I. Allakhverdiev,Suleyman I. Allakhverdiev +11 more
TL;DR: A detailed assessment of the chemistry of Mn oxides by considering how their bulk and nanoscale properties contribute to their effectiveness as water-oxidizing catalysts and the issue of Mn complexes decomposing to Mn oxide is provided.
Journal ArticleDOI
The Structure of Photosystem II and the Mechanism of Water Oxidation in Photosynthesis
TL;DR: The overall structure of PSII is provided followed by detailed descriptions of the specific structure of the Mn4CaO5 cluster and its surrounding protein environment, based on the geometric organization revealed by the crystallographic analysis.
Journal ArticleDOI
A metalloradical mechanism for the generation of oxygen from water in photosynthesis
TL;DR: A model is proposed whereby the tyrosyl radical functions by abstracting hydrogen atoms from substrate water bound as terminal ligands to two of the four manganese ions, establishing clear analogies between photosynthetic water oxidation and amino acid radical function in other enzymatic reactions.
References
More filters
Journal ArticleDOI
A highly resolved, oxygen-evolving photosystem II preparation from spinach thylakoid membranes
TL;DR: The properties of oxygenevolving PS II preparations obtained by detergent resolution of chloroplast thylakoid membranes are reported.
Journal ArticleDOI
Cooperation of charges in photosynthetic o2 evolution–i. a linear four step mechanism
TL;DR: The evolution of O2 in weak light and light flashes is studied to analyze the interactions between light induced O2 precursors and their decay in darkness and the data are compatible with a linear four step mechanism in which a trapping center successively accumulates four + charges.
Journal ArticleDOI
Isolation of a photosystem II reaction center consisting of D-1 and D-2 polypeptides and cytochrome b-559.
Osamu Nanba,Kimiyuki Satoh +1 more
TL;DR: Results strongly suggest that the site of primary charge separation in photosystem II is located on the heterodimer composed of D-1 and D-2 subunits.
Journal ArticleDOI
Directed mutagenesis indicates that the donor to P 680+ in photosystem II is tyrosine-161 of the D1 polypeptide
TL;DR: Results provide strong support for the identification of Tyr-161 in the D1 polypeptide with YZ, and the nature of the fluorescence change indicates that forward electron transfer to P+680 is disrupted in the mutant.
Journal ArticleDOI
Site-directed mutagenesis identifies a tyrosine radical involved in the photosynthetic oxygen-evolving system
TL;DR: It is suggested that the C2 symmetry in photosystem II extends beyond P680 to its immediate electron donor and concluded that Z is Tyr-161 of the D1 polypeptide, which is probably a second tyrosine located in a similar environment.