Electron transfer from Cyt b (559) and tyrosine-D to the S2 and S3 states of the water oxidizing complex in photosystem II at cryogenic temperatures

Feyziyev, Y.; Deák, Z.; Styring, Sörn.; Bernát, Gábor.

Journal of Bioenergetics and Biomembranes 45(1-2): 111-120

2013


ISSN/ISBN: 0145-479X
PMID: 23104119
DOI: 10.1007/s10863-012-9482-8
Accession: 052926292

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Abstract
The Mn4CaO5 cluster of photosystem II (PSII) catalyzes the oxidation of water to molecular oxygen through the light-driven redox S-cycle. The water oxidizing complex (WOC) forms a triad with TyrosineZ and P680, which mediates electrons from water towards the acceptor side of PSII. Under certain conditions two other redox-active components, TyrosineD (YD) and Cytochrome b559 (Cyt b559) can also interact with the S-states. In the present work we investigate the electron transfer from Cyt b559 and YD to the S2 and S3 states at 195 K. First, YD and Cyt b559 were chemically reduced. The S2 and S3 states were then achieved by application of one or two laser flashes, respectively, on samples stabilized in the S1 state. EPR signals of the WOC (the S2-state multiline signal, ML-S2), YD and oxidized Cyt b559 were simultaneously detected during a prolonged dark incubation at 195 K. During 163 days of incubation a large fraction of the S2 population decayed to S1 in the S2 samples by following a single exponential decay. Differently, S3 samples showed an initial increase in the ML-S2 intensity (due to S3 to S2 conversion) and a subsequent slow decay due to S2 to S1 conversion. In both cases, only a minor oxidation of YD was observed. In contrast, the signal intensity of the oxidized Cyt b559 showed a two-fold increase in both the S2 and S3 samples. The electron donation from Cyt b559 was much more efficient to the S2 state than to the S3 state.

Electron transfer from Cyt b(559) and tyrosine-D to the S2 and S3 states of the water oxidizing complex in photosystem II at cryogenic temperatures