Photoassembly of the manganese cluster and oxygen evolution from monomeric and dimeric CP47 reaction center photosystem II complexes
AUTOR(ES)
Büchel, Claudia
FONTE
The National Academy of Sciences
RESUMO
Isolated subcomplexes of photosystem II from spinach (CP47RC), composed of D1, D2, cytochrome b559, CP47, and a number of hydrophobic small subunits but devoid of CP43 and the extrinsic proteins of the oxygen-evolving complex, were shown to reconstitute the Mn4Ca1Clx cluster of the water-splitting system and to evolve oxygen. The photoactivation process in CP47RC dimers proceeds by the same two-step mechanism as observed in PSII membranes and exhibits the same stoichiometry for Mn2+, but with a 10-fold lower affinity for Ca2+ and an increased susceptibility to photodamage. After the lower Ca2+ affinity and the 10-fold smaller absorption cross-section for photons in CP47 dimers is taken into account, the intrinsic rate constant for the rate-limiting calcium-dependent dark step is indistinguishable for the two systems. The monomeric form of CP47RC also showed capacity to photoactivate and catalyze water oxidation, but with lower activity than the dimeric form and increased susceptibility to photodamage. After optimization of the various parameters affecting the photoactivation process in dimeric CP47RC subcores, 18% of the complexes were functionally reconstituted and the quantum efficiency for oxygen production by reactivated centers approached 96% of that observed for reconstituted photosystem II-enriched membranes.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=24429Documentos Relacionados
- Assembly of the D1 precursor in monomeric photosystem II reaction center precomplexes precedes chlorophyll a-triggered accumulation of reaction center II in barley etioplasts.
- Investigation of the structure of trimeric and monomeric photosystem I reaction centre complexes
- Nucleotide sequences of psbB and psbH, the plastid encoded genes for CP47 and the 10 kDa phosphoprotein of photosystem II in Oenothera hookeri and argillicola.
- Monomeric and trimeric forms of photosystem I reaction center of Mastigocladus laminosus: crystallization and preliminary characterization.
- Proximity of the manganese cluster of photosystem II to the redox-active tyrosine YZ.