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

• The effect of oxygen and anaerobiosis on the redox properties of Cyt b559 was investigated in PSII prepns. 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 CaCl2 washed), Cl depleted and after complete depletion of the Mn cluster (Tris washed). In active PSII centers, about 75% of Cyt b559 was found in the high-potential form and the rest in the intermediate potential form. With decompn. 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 b559 into the low-potential and high-potential forms was only obsd. after treatments that directly affect the Mn cluster. In PSII membranes, deprived of all three extrinsic subunits (CaCl2 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%, resp. In intact PSII membranes, the oxygen-dependent conversion did not occur. The possible physiol. role of this oxygen-dependent behavior of the Cyt b559 redox forms during the assembly/photoactivation cycle of PSII is discussed.

Ämnesord

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Nyckelord

Photosystem

Cytochrome

Chemistry

Kemi

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