Oxygen‐induced changes in the redox state of the cytochrome b₅₅₉ in photosystem II depend on the integrity of the Mn cluster

Abstract

The effect of oxygen and anaerobiosis on the redox properties of Cyt b(559) was investigated in PSII preparations from spinach with different degree of disintegration of the donor side. Comparative studies were performed on intact PSII membranes and PSII membranes that were deprived of the 18-kDa peripheral subunit (0.25 NaCl washed), the 18- and 24-kDa peripheral subunits (1 M NaCl washed), the 18-, 24- and 33-kDa peripheral subunits (1.2 M CaCl(2) washed), Cl depleted and after complete depletion of the Mn cluster (Tris washed). In active PSII centers, about 75% of Cyt b(559) was found in the high-potential form and the rest in the intermediate potential form. With decomposition of the donor side, the intermediate potential form started to dominate, reaching more than 90% after Tris treatment. The oxygen-dependent conversion of the intermediate potential form of Cyt b(559) into the low-potential and high-potential forms was only observed after treatments that directly affect the Mn cluster. In PSII membranes, deprived of all three extrinsic subunits (CaCl(2) treatment), 21% of the intermediate potential form was converted into the low-potential form and 14% into the high-potential form by the removal of oxygen. In Tris-washed PSII membranes, completely lacking the Mn cluster, this conversion amounted to 60 and 33%, respectively. In intact PSII membranes, the oxygen-dependent conversion did not occur. The possible physiological role of this oxygen-dependent behavior of the Cyt b(559) redox forms during the assembly/photoactivation cycle of PSII is discussed.

Formation of tyrosine radicals in photosystem II under far-red illumination

“…The Mn 4 CaO 5 cluster and extrinsic subunits were removed by the Tris washing (Gadjieva et al 1999 , Mamedov et al 2007 ). PS II membranes were resuspended in 1.0 M Tris buffer at pH 9.1 with Chl concentration 1 mg/mL.…”

“…The slow oxidation behavior of Tyr D makes it possible to study by the conventional EPR spectroscopy while Tyr Z oxidation kinetics is too fast to be followed. Different biochemical treatment such as Tris and NH 2 OH washing can remove the Mn 4 CaO 5 cluster and extrinsic proteins, leaving PS II core exposed to the lumen (Boussac and Etienne 1982b ; Gadjieva et al 1999 ; Mamedov et al 2007 ). This makes Tyr Z oxidation to slow down by two or three orders of magnitude (t 1/2 = 20–600 ms) (Buser et al 1990 ).…”

Role of Novel Dimeric Photosystem II (PSII)-Psb27 Protein Complex in PSII Repair

“…The S 2 state multiline EPR signal from the CaMn 4 cluster was induced by illumination at 200 K for 6 min (23). The total manganese content in the samples, measured at room temperature, was estimated after extraction with 200 mM HNO 3 and 100 mM CaCl 2 as described previously (37). Spectral analysis was performed using Bruker Xepr 2.1 software.…”

Putative function of cytochrome b559 as a plastoquinol oxidase

“…pH changes or photoinhibitory conditions. It has also been shown recently that the different potential forms of cyt b559 are interconvertible in Tris‐treated PSII membranes in an O 2 ‐dependent manner (Mamedov et al 2007). Tiwari and Pospisil (2009) showed that cyt b559 is converted by O 2 − after tens of seconds illumination from the intermediate into the high potential form and then, after longer illumination (more than 100 s) in a lower potential form.…”