Putative function of cytochrome b559 as a plastoquinol oxidase.

The function of cytochrome b559 (cyt b559) in photosystem II (PSII) was studied in a tobacco mutant in which the conserved phenylalanine at position 26 in the beta-subunit was changed to serine. Young leaves of the mutant showed no significant difference in chloroplast ultra structure or in the amount and activity of PSII, while in mature leaves the size of the grana stacks and the amount of PSII were significantly reduced. Mature leaves of the mutant showed a higher susceptibility to photoinhibition and a higher production of singlet oxygen, as shown by spin trapping electron paramagnetic resonance (EPR) spectroscopy.

Manganese binding to the 23 kDa extrinsic protein of Photosystem II.

The recombinant form of the extrinsic 23 kDa protein (psbP) of Photosystem II (PSII) was studied with respect to its capability to bind Mn. The stoichiometry was determined to be one manganese bound per protein. A very high binding constant, K(A)=10(-17) M(-1), was determined by dialysis of the Mn containing protein against increasing EDTA concentration.

Function of the 23 kDa extrinsic protein of Photosystem II as a manganese binding protein and its role in photoactivation.

The function of the extrinsic 23 kDa protein of Photosystem II (PSII) was studied with respect to Mn binding and its ability to supply Mn to PSII during photoactivation, i.e. the light-dependent assembly of the tetramanganese cluster.

Production of reactive oxygen species in chloride- and calcium-depleted photosystem II and their involvement in photoinhibition.

Mixed photosystem II (PSII) samples consisting of Cl(-)-depleted and active, or Ca(2+)-depleted and active PSII enriched membrane fragments, respectively, were investigated with respect to their susceptibility to light. In the presence of Cl(-)-depleted PSII, active centers were damaged more severely, most likely caused by a higher amount of reactive oxygen species formed in the nonfunctional centers. Cl(-) depletion led to an increased H(2)O(2) production, which seemed to be responsible for the stimulation of PSII activity loss.

Evidence that cytochrome b559 mediates the oxidation of reduced plastoquinone in the dark.

The function of cytochrome b(559) in photosystem II (PSII) was investigated using a mutant created in tobacco in which the conserved phenylalanine at position 26 in the beta-subunit (PsbF) was changed to serine (Bock, R., Kössel, H., and Maliga, P.