Restoration and Interaction of Cytochrome c with Short-Term UV-Irradiated Preparations of Manganese-Stabilizing Protein PsbO and PS II Membranes

The interaction of cytochrome c with UV-irradiated manganese-stabilizing protein PsbO and PS II membranes has been studied. It has been established that UV-irradiated PsbO protein is capable of restoring cytochrome c, and this process is inhibited by superoxide dismutase and stimulated by catalase, which indicates the involvement of reactive oxygen species. A similar reduction of cytochrome c was observed upon the addition of UV-irradiated tyrosine or cystine solutions, which confirms the role of amino acid radicals in this process. It has been demonstrated that UV irradiation causes the dimerization of the PsbO protein. After incubation with cytochrome c for 24 hours, the dimer level decreases, restoring the concentration of monomers. UV-irradiated PS II membranes also restore cytochrome c, and the reduction activity depends on the presence of PsbO in PS II. Oxidized cytochrome c binds more strongly to the PsbO protein and photosystem II than restored cytochrome c. These data suggest that UV irradiation generates reactive groups in the PsbO protein, both in isolated form and as part of photosystem II, that restore cytochrome c. Additionally, irradiation of PsbO protein in solution leads to the formation of intermediate products involving reactive oxygen species, which oxidize restored cytochrome c.