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pH sensitivity of the redox state of cytochrome b559 may regulate its function as a protectant against donor and acceptor side photoinhibition


, : pH sensitivity of the redox state of cytochrome b559 may regulate its function as a protectant against donor and acceptor side photoinhibition. Photosynthesis Research 46(1-2): 193-202

A series of experiments have been conducted with isolated reaction centers of photosystem two (PS II) with the aim to elucidate the functional role of cytochrome b-559 (Cyr b-559). At pH 6.5 it was found that Cyt b-559 was reversibly photoreduced by red actinic light when Mn-2+ was present as an electron donor while at pH 8.5 a photo-oxidation was observed under the same lighting conditions, which was dark reversible in the presence of hydroquinone. These pH dependent light induced changes were measured under anaerobic conditions and correlated with changes in the relative levels of high (HP) and low (LP) potential forms of the cytochrome, At pH 6.5 the cytochrome was mainly in its LP form while at pH 8.5 a-significant proportion was converted to the HP form as detected by dark titrations with hydroquinone. This pH dependent difference in the levels of HP and LP Cyt b-559 was also detected when bright white light was used to monitor the level of the LP form using a novel reaction involving direct electron donation from the flavin of glucose oxidase (present in the medium and used together with glucose and catalase as an oxygen trap). The results suggest that PS II directly oxidises and reduces the HP and LP forms, respectively and that the extent of these photo-reactions is dependent on the relative levels of the two forms, which are in turn governed by the pH. This conclusion is interpreted in terms of the model presented previously (Barber J and De Las Rivas J (1993) Proc Natl Acad Set USA 90: 10942-10946) whereby the pH induced effect is considered as a possible mechanism by which interconvers on of LP and HP forms of Cyt b-559 is achieved. In agreement with this was the finding that as the extent of photo-oxidisable HPCyt b-559 increases, with increasing pH, the rate of irreversible photo-oxidation of beta-carotene decreases, a result expected if the HP form protects against donor side photoinhibition.

Accession: 002914517

PMID: 24301582

DOI: 10.1007/BF00020430

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Related references

Barber, J.; D.L.s Rivas, J., 1993: A functional model for the role of cytochrome b559 in the protection against donor and acceptor side photoinhibition. A quinone-independent photoreduction of the low potential form of cytochrome b-559 has been studied using isolated reaction centers of photosystem II. Under anaerobic conditions, the cytochrome can be fully reduced by exposure to strong illuminati...

Lazár, D.; Ilík, P.; Kruk, J.; Strzałka, K.; Naus, J., 2004: A theoretical study on effect of the initial redox state of cytochrome b559 on maximal chlorophyll fluorescence level (F(M)): implications for photoinhibition of photosystem II. In this work, we extended the reversible radical pair model which describes energy utilization and electron transfer up to the first quinone electron acceptor (QA) in photosystem II (PSII), by redox reactions involving cytochrome (cyt) b559. In th...

Napiwotzki, A.; Bergmann, A.; Decker, K.; Legall, H.; Eckert, H.-Joerg; Eichler, H.-Joachim; Renger, G., 1997: Acceptor side photoinhibition in PS II: On the possible effects of the functional integrity of the PS II donor side on photoinhibition of stable charge separation. Photoinhibition under aerobic and anaerobic conditions was analyzed in O-2-evolving and in Tris-treated PS II-membrane fragments from spinach by measuring laser-flash-induced absorption changes at 826 nm reflecting the transient P680+ formation an...

Kaminskaya, O.P.; Shuvalov, V.A., 2013: Biphasic reduction of cytochrome b559 by plastoquinol in photosystem II membrane fragments: evidence for two types of cytochrome b559/plastoquinone redox equilibria. In photosystem II membrane fragments with oxidized cytochrome (Cyt) b559 reduction of Cyt b559 by plastoquinol formed in the membrane pool under illumination and by exogenous decylplastoquinol added in the dark was studied. Reduction of oxidized C...

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Hideg, E.; Spetea, C.; Vass, I., 1994: Singlet oxygen and free radical production during acceptor-and donor-side-induced photoinhibition: Studies with spin trapping EPR spectroscopy. High-intensity illumination of thylakoids results in the well-characterized impairment of Photosystem II electron transport (photoinhibition), followed by the degradation of the D1 reaction centre protein. The time-course and features of photodama...

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