Electron Transfer on the Donor Side of Manganese-Depleted Photosystem 2статья
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Дата последнего поиска статьи во внешних источниках: 11 ноября 2019 г.
Аннотация:After removal of manganese ions responsible for lightdriven water oxidation, redoxactive tyrosine YZ (tyrosine 161 of the D1 subunit) still remains the dominant electron donor to the photooxidized chlorophyll P680 (P+680) in the reaction center of photosystem 2 (PS2). Here, we investigated P+680 reduction by YZ under singleturnover flashes in Mn-depleted PS2 core complexes in the presence of weak acids and NH4Cl. Analysis of changes in the lightinduced absorption at 830 nm (reflecting P680 redox transitions) at pH 6.0 showed that P+680 reduction is well approximated by two kinetic components with the characteristic times (τ) of ~7 and ~31 μs and relative contributions of ~54 and ~37%, respectively. In contrast to the very small effect of sodium formate (200 mM), addition of sodium acetate and NH4Cl increased the rate of electron transfer between YZ and P+680 approx. by a factor of 5. The suggestion that direct electron transfer from YZ to P+680 has a biphasic kinetics and reflects the presence of two different populations of PS2 centers was confirmed by the data obtained
using direct electrometrical technique. It was demonstrated that the submillisecond twophase kinetics of the additional electrogenic phase in the kinetics of photoelectric response due to the electron transfer between YZ and P+ 680 is significantly accelerated in the presence of acetate or ammonia. These results contribute to the understanding of the mechanism of interaction between the oxidized tyrosine YZ and exogenous substances (including synthetic manganesecontaining compounds)
capable of photooxidation of water molecule in the manganesedepleted PS2 complexes.