Electron transfer from Cyt b (559) and tyrosine-D to the S-2 and S-3 states of the water oxidizing complex in photosystem II at cryogenic temperatures
2013 (English)In: Journal of Bioenergetics and Biomembranes, ISSN 0145-479X, E-ISSN 1573-6881, Vol. 45, no 1-2, 111-120 p.Article in journal (Refereed) Published
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 Tyrosine(Z) and P-680, which mediates electrons from water towards the acceptor side of PSII. Under certain conditions two other redox-active components, Tyrosine(D) (Y-D) and Cytochrome b (559) (Cyt b (559)) can also interact with the S-states. In the present work we investigate the electron transfer from Cyt b (559) and Y-D to the S-2 and S-3 states at 195 K. First, Y-D (aEuro cent) and Cyt b (559) were chemically reduced. The S-2 and S-3 states were then achieved by application of one or two laser flashes, respectively, on samples stabilized in the S-1 state. EPR signals of the WOC (the S-2-state multiline signal, ML-S-2), Y-D (aEuro cent) and oxidized Cyt b (559) were simultaneously detected during a prolonged dark incubation at 195 K. During 163 days of incubation a large fraction of the S-2 population decayed to S-1 in the S-2 samples by following a single exponential decay. Differently, S-3 samples showed an initial increase in the ML-S-2 intensity (due to S-3 to S-2 conversion) and a subsequent slow decay due to S-2 to S-1 conversion. In both cases, only a minor oxidation of Y-D was observed. In contrast, the signal intensity of the oxidized Cyt b (559) showed a two-fold increase in both the S-2 and S-3 samples. The electron donation from Cyt b (559) was much more efficient to the S-2 state than to the S-3 state.
Place, publisher, year, edition, pages
2013. Vol. 45, no 1-2, 111-120 p.
EPR, Photosystem II, Water oxidation, S-states, Tyrosine radical, Cytochrome b(559)
IdentifiersURN: urn:nbn:se:uu:diva-196550DOI: 10.1007/s10863-012-9482-8ISI: 000314899500010OAI: oai:DiVA.org:uu-196550DiVA: diva2:610813