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. (1994) EMBO J. 13, 4623-4628). The mutant grew photoautotrophically, but the amount of PSII was reduced and the ultrastructure of the chloroplast was dramatically altered. Very few grana stacks were formed in the mutant. Although isolated PSII-enriched membrane fragments showed low PSII activity, electron paramagnetic resonance indicated the presence of functional PSII. Difference absorption spectra showed that the cytochrome b(559) contained heme. The plastoquinone pool was largely reduced in dark-adapted leaves of the mutant, based on chlorophyll fluorescence and thermoluminescence measurements. We therefore propose that cytochrome b(559) plays an important role in PSII by keeping the plastoquinone pool and thereby the acceptor side of PSII oxidized in the dark. Structural alterations as induced by the single Phe --> Ser point mutation in the transmembrane domain of PsbF evidently inhibit this function.
Bondarava
Natallia
N
Institut für Biologie II, Biochemie der Pflanzen, Universität Freiburg, Schänzlestrasse 1, 79104 Freiburg, Germany.
De Pascalis
Luca
L
Al-Babili
Salim
S
Goussias
Charilaos
C
Golecki
Jochen R
JR
Beyer
Peter
P
Bock
Ralph
R
Krieger-Liszkay
Anja
A
D002734:Chlorophyll / Q000378:metabolism*; D003573:Cytochrome b Group / Q000378:metabolism* / Q000648:ultrastructure; D003624:Darkness; D008027:Light; D008163:Luminescent Measurements; D008854:Microscopy, Electron; D010084:Oxidation-Reduction; D045332:Photosystem II Protein Complex; D018515:Plant Leaves / Q000378:metabolism / Q000648:ultrastructure; D010971:Plastoquinone / Q000378:metabolism*; D021122:Protein Subunits / Q000378:metabolism; D014026:Nicotiana / Q000378:metabolism*
D003573:Cytochrome b Group; D045332:Photosystem II Protein Complex; D021122:Protein Subunits; D002734:Chlorophyll; C019313:cytochrome b559; D010971:Plastoquinone