| Autor: |
Semin BК; Department of Biophysics, Faculty of Biology, Lomonosov Moscow State University, Moscow, Russia, 119234. semin@biophys.msu.ru., Davletshina LN; Department of Biophysics, Faculty of Biology, Lomonosov Moscow State University, Moscow, Russia, 119234., Goryachev SN; Department of Biophysics, Faculty of Biology, Lomonosov Moscow State University, Moscow, Russia, 119234., Seibert M; Laboratory, BioEnergy Sciences and Technology Directorate, National Renewable Energy, Golden, CO, 80401, USA. |
| Jazyk: |
angličtina |
| Zdroj: |
Photosynthesis research [Photosynth Res] 2021 Feb; Vol. 147 (2), pp. 229-237. Date of Electronic Publication: 2021 Feb 02. |
| DOI: |
10.1007/s11120-020-00813-z |
| Abstrakt: |
Fe(II) cations bind with high efficiency and specificity at the high-affinity (HA), Mn-binding site (termed the "blocking effect" since Fe blocks further electron donation to the site) of the oxygen-evolving complex (OEC) in Mn-depleted, photosystem II (PSII) membrane fragments (Semin et al. in Biochemistry 41:5854, 2002). Furthermore, Fe(II) cations can substitute for 1 or 2Mn cations (pH dependent) in Ca-depleted PSII membranes (Semin et al. in Journal of Bioenergetics and Biomembranes 48:227, 2016; Semin et al. in Journal of Photochemistry and Photobiology B 178:192, 2018). In the current study, we examined the effect of Ca 2+ cations on the interaction of Fe(II) ions with Mn-depleted [PSII(-Mn)] and Ca-depleted [PSII(-Ca)] photosystem II membranes. We found that Ca 2+ cations (about 50 mM) inhibit the light-dependent oxidation of Fe(II) (5 µM) by about 25% in PSII(-Mn) membranes, whereas inhibition of the blocking process is greater at about 40%. Blocking of the HA site by Fe cations also decreases the rate of charge recombination between Q A - and Y Z •+ from t 1/2 = 30 ms to 46 ms. However, Ca 2+ does not affect the rate during the blocking process. An Fe(II) cation (20 µM) replaces 1Mn cation in the Mn 4 CaO 5 catalytic cluster of PSII(-Ca) membranes at pH 5.7 but 2 Mn cations at pH 6.5. In the presence of Ca 2+ (10 mM) during the substitution process, Fe(II) is not able to extract Mn at pH 5.7 and extracts only 1Mn at pH 6.5 (instead of two without Ca 2+ ). Measurements of fluorescence induction kinetics support these observations. Inhibition of Mn substitution with Fe(II) cations in the OEC only occurs with Ca 2+ and Sr 2+ cations, which are also able to restore oxygen evolution in PSII(-Ca) samples. Nonactive cations like La 3+ , Ni 2+ , Cd 2+ , and Mg 2+ have no influence on the replacement of Mn with Fe. These results show that the location and/or ligand composition of one Mn cation in the Mn 4 CaO 5 cluster is strongly affected by calcium depletion or rebinding and that bound calcium affects the redox potential of the extractable Mn4 cation in the OEC, making it resistant to reduction. |
| Databáze: |
MEDLINE |
| Externí odkaz: |
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